CHEMISTRY FORM ONE STUDY NOTES TOPIC 5: MATTER, TOPIC 6: AIR COMBUSTION, RUSTING AND FIRE FIGHTING.

TOPIC 5: MATTER

Concept of matter

Concept of Matter

Explain concept of matter

Matter is anything that has mass and occupies space. Therefore, anything around us provided it has mass and can occupy the space, is termed as matter. There are many kinds of matter. Can you mention some? The word matter is used to cover all the substances and materials from which the earth and universe is composed of. These include all materials around us such as water, soil, plants, animals, air, clothes, etc.

Any particular kind of matter is called a substance. Substances include elements and compounds. An element is a substance which is the limit of chemical analysis. When two or more elements are combined chemically, a compound is formed. Matter is made up of atoms, ions or molecules. You will learn more about this later.

States of matter

The Three States of Matter

Describe the three states of matter

Any chemical substance we study exists in any of the three forms (or physical states). The three different states of matter are

1. solid state
2. liquid state and
3. gaseous states

So, each of the many millions of substances around us can be classified as a solid, a liquid or gas. Look around you and name substances that are solids, liquids and gases. The state in which any matter exists depends on temperature and sometimes pressure conditions. One substance may exist as a solid in one condition and as a liquid or gas under a different condition. Water is an example of such substances. This change is called a change in the state of matter.

The three physical states of matter differ in the way they respond to temperature and pressure. All three states can increase in volume (expansion) when the temperature is increased. They decrease in volume (contraction) when the temperature is decreased. Gases are easily compressed. Liquids are only slightly compressible. Solids are incompressible. They are not affected by change in pressure.

Investigation of the compressibility of solids, liquids and gases

Procedure

1. Take three new syringes and fill them with sand, water and air respectively (figure 5.1).
2. Try to push in the end of each syringe.
3. Observe what happens.

Figure

Compressibility of solids, liquids and gases

Observation

Which of the substances under investigation can compress into a smaller volume?

Findings

You should have found that a solid (sand) and a liquid (water) cannot be compressed but a gas (air) is easily compressed.

The three states of matter differ in their physical properties. These differences in properties are summarized in table bellow

Differences in properties of the three states of matter

Property	Physical state
	Solid	Liquid	Gas
Shape	has a definite shape	no definite shape, takes shape of the container	no definite shape, occupy whole container
Volume	has a fixed volume	has a fixed volume	variable (depending on temperature and pressure)
Fluidity	does not flow	generally flows easily	flows easily
Expansion on heating	low	medium	high
Compressibility	incompressible	almost incompressible	highly compressible
Motion of particles	slow	high	very high
Density	high	moderate to high	low
Tangibility	tangible	tangible	intangible
Visibility	visible	visible	invisible

One State of Matter to Another

Change one state of matter to another

We have seen that matter exists in three different states - solids, liquids and gases. We can use the kinetic theory of matter to explain how a substance changes from one state to another. Basically, changes from one state to another are caused by alterations in temperature and pressure. Normally molecules, ions or atoms of a substance move faster when the temperature is increased.

Melting and freezing

Melting is a change from solid to liquid state. When solids are heated, their constituent particles (atoms, molecules or ions) get energy and vibrate more violently. Vibrations of these particles overcome (exceed) their binding forces. The particles become mobile. The crystalline structure of solid is destroyed. A liquid state is reached and the particles are free to move. The temperature at which this happens is called melting point of the solid.

The melting point of a solid tells us something about the strength of forces holding its constituent particles together. Substances with high melting points have strong forces between their particles. Those with low melting points have weak forces between their particles.

Change in state from solid to liquid

Freezing is a change from liquid to solid state. Freezing is the opposite of melting. The process is reversed at the same temperature if a liquid is cooled. The temperature at which a substance turns to a solid is called freezing point. The melting point and freezing point of any given substance are both the same. For example, the melting and freezing of pure water takes place at 0°C. Melting is not affected by any changes in atmospheric pressure.

Evaporation and boiling

Boiling is a change from liquid to vapour state at a particular temperature. Evaporation is the change from liquid to vapour state at any given temperature. If a liquid is exposed to open air, it evaporates. Splashes of water evaporate at room temperature. After rain, small pools of water dry up. When a liquid changes into a gas at any temperature, the process is called evaporation. Evaporation takes places from the surface of the liquid. The larger the surface area, the faster the liquid evaporates. The warmer the liquid is, the faster it evaporates. Thus, surface area and temperature affects the rate of evaporation of a liquid.

When a liquid is heated, its molecules get more energy and move faster. They knock into each other violently and bounce further apart. As the heating goes on, its molecules vibrate even faster. Bubbles of gas (due to air dissolved in water) appear inside the liquid. The whole process is called boiling. The temperature at which a liquid boils is called boiling point.

The molecules at the surface of the liquid gain enough energy to overcome the forces holding them together. They break away from the liquid and from a gas (vapour). As more of the liquid molecules escape to form a gas, a liquid is said to evaporate. This occurs at the boiling point of a liquid.

Change in state from liquid to gas

The temperature at which a liquid boils explains how strong the forces holding its particles (molecules) together are. Liquids with high boiling points have strong forces of attraction between their molecules than those liquids with low boiling points.

The boiling point of a liquid can change if the surrounding pressure changes. If the surrounding pressure falls, the boiling point also falls. The boiling point of water at standard pressure (760 mmHg) is 100°C. On a high mountain, where pressure is low, it is lower than 100°C. If the surrounding pressure is increased, the boiling point rises. The same behaviour is experienced by a gas when the pressure is either increased or decreased.

The melting and boiling points of some common chemical substances at standard temperature and pressure (s.t.p)

Substance	Physical state at room temperature (20°C)	Melting point (°C)	Boiling point(°C)
Oxygen	gas	-219	-183
Nitrogen	gas	-210	-196
Ethanol (alcohol)	liquid	-117	78
Water	liquid	0	100
Sulphur	solid	115	444
Common salt (sodium chloride)	solid	801	1465
Copper	solid	1083	2600
Carbon dioxide	gas	sublimation point (°C): -78

From the above explanation, obvious differences between evaporation and boiling can be detected. See table bellow

Evaporation	Boiling
1.Occurs at all temperatures	Occurs at one particular temperature (boiling point)
2.Occurs on the surface of the liquid	Occurs both inside and on the surface of the liquid
3.Takes place slowly	Takes place faster
4.Bubbles are not necessarily formed	Bubbles are formed

Therefore, the two terms can be defined as follows: Evaporation is a change in state of a substance from liquid to gas (vapour) state at any temperature.

Boiling is a change in state of a substance from liquid to gas at a particular temperature and pressure.

Condensation and solidification

The reverse of evaporation is condensation. This is brought about by cooling. When a gas is cooled down, its particles lose energy. They move more and more slowly. When they knock into each other, they do not have enough energy to bounce away again. They stay close together and a liquid forms. This process is called condensation. When the liquid is cooled further, the movement of the particles slows down even more. Eventually, they stop moving and a solid forms. This is called solidification.

Condensation can be defined as a change in state of a substance from gas (vapour) to liquid. Solidification is a change from liquid to solid state of a substance. Solidification is the same as freezing.

Sublimation

A few solids do not melt when they are heated. Instead, they change directly from the solid to gaseous state without passing through the liquid state. This change in state is called sublimation. When a solid changes directly into gas, it is said to sublime. Iodine, solid carbon dioxide ("dry ice") and ammonium chloride are examples of solids that sublime. Like melting, sublimation also occurs at one particular temperature for each pure solid.

The Importance of Changing One State of Matter to Another

Explain the importance of changing one state of matter to another

The following points summarize the importance of change in state:

1. Separation of mixtures

Different mixtures can be separated through such processes as distillation, sublimation, evaporation and condensation. Let us have a look at an example of distillation. This process involves boiling, evaporation and condensation. Distillation as a process can be applied in separation of a mixture (solution) of two or more substances. A mixture of two or more substances with different boiling points e.g. water and alcohol can be separated by this means. In such a case, a container with the mixed-up liquids is heated. The liquid with a low boiling point evaporates and condenses first, leaving the one with a high boiling point in the container. The distillate (liquid with low boiling point) is collected, cooled down and transferred into another container.

2. Industrial manufacture of products

Industrially, the process of distillation is applied in the production of pure substances such as beer and other alcoholic drinks such as wine, vodka, konyagi, etc. The manufacturing process involves boiling, evaporating and condensation.

3. Refining of petroleum (crude oil)

Crude oil contains organic liquid components, each with a different boiling point. In the refinery, the components with lower boiling points evaporate first and get separated out, leaving those with higher boiling points behind. In this way, we get various types of oil components (fractions) such as petrol, diesel, kerosene, lubricating oil, etc.

4. Drying of crops and clothes

When you suspend your clothing on a cloth line to dry, the moisture in it is lost through evaporation. Likewise, farmers in the village often spread crops on the ground to dry. They do this in order to reduce moisture content and hence prevent decaying. The moisture contained in crops leave by evaporation. Therefore, you can notice how evaporation, as a change in state, is important in everyday lives.

5. Cooling of our bodies in hot weather

You all like to drink cold water or beverages especially during hot weather. You can use a refrigerator to cool down drinking water or beverages directly. Alternatively, you can freeze water into ice and then use the resulting ice for cooling the beverage. Ice blocks are also saleable. Moreover, one can earn some money if she freezes water into ice blocks and then sells them to beverage vendors. Perishable products such as fish, meat, milk, etc are often packed in ice blocks to prevent them from going bad. Ice, as we studied early, is formed when water freezes (a change in state from liquid to solid).

6. Ice formation in refrigerators

You all like to drink cold water or beverages especially during hot weather. You can use a refrigerator to cool down drinking water or beverages directly. Alternatively, you can freeze water into ice and then use the resulting ice for cooling the beverage. Ice blocks are also saleable. Moreover, one can earn some money if she freezes water into ice blocks and then sells them to beverage vendors. Perishable products such as fish, meat, milk, etc are often packed in ice blocks to prevent them from going bad. Ice, as we studied early, is formed when water freezes (a change in state from liquid to solid).

7. Melting metals to make alloys

In metallurgical industries, need may arise to mix two or more metals (alloys) together. This is only possible, where two or more metals are first melted at high temperatures into liquids. Then the resulting liquid metals are mixed in appropriate proportions. This is followed by cooling down the mixture to a solid alloy. Normally alloys have better qualities than individual metals.

8. Testing the purity of substances

The presence of impurity may lower or raise the boiling point of the substance. A pure substance melts and boils at definite temperatures (see table 5.4). The values for the melting point and boiling point are precise and predictable. This means that we can use them to test the purity of a sample. They can also be used to check the identity of unknown substance.

A typical example

Sea water is impure. It freezes at a temperature well below the freezing point of pure water (0°C) and boils at a temperature above the boiling point of pure water (100°C). Other substances behave in a similar manner. So, boiling as a change in state can be used to test for the purity of a substance.

In addition, the impurity also reduces the exactness of the melting or boiling point. An impure substance melts or boils over a range of temperature, not at a particular point.

Melting and boiling points of some pure substances

Substance	Melting point (°C)	Boiling point (°C)
Water	0	100
Ethanol	-117	78
Oxygen	-219	-183
Sodium	98	890
Sulphur	119	445
Iron	1540	2900
Diamond	3550	4832
Cobalt	1492	2900
Nitrogen	-210	-196
Propane	-188	- 42
Ethanoic acid	16	118

9. Formation of rain

Perhaps the most important of all, as far as change in state is concerned, is the formation of rain. Rained is mainly formed through the process of evaporation and condensation. Water vapour, evaporating mostly from water bodies (oceans, seas, lakes, rivers, ponds, etc), land and plants rises up to the sky. As it rises, it cools down and condenses into tiny droplets

On further cooling as they rise up, these droplets form bigger water drops. Owing to gravitational force, these drops fall down as rainfall. Every one of you knows how important rain is to our life. Therefore, you have noticed how evaporation and condensation, as changes in state, contribute to rain formation.

Rain formation

Kinetic nature of matter

We already know that matter is composed of atoms, ions or molecules. We have not yet considered the reason why the same substance, say water, can exist in more than one form, for example as solid ice, liquid water, and gaseous steam. But does matter behave like that?

The kinetic theory of matter has been used to explain the way in which the arrangement of the particles of a substance can determine the properties of that substance, and particularly the state in which it is likely to be found under a given set of conditions. The idea is that all matter is made up of tiny moving particles. The main points of the theory are as follows:

1. All matter is made up of tiny particles (atoms and molecules) that are invisible to the naked eye and to most microscopes.
2. The particles are moving all the time. The higher the temperature is, the higher the average energy of the particles.
3. Heavier particles move more slowly than lighter particles at the same temperature.
4. Each substance has unique particles that are different from the particles of other substances.
5. The particles of matter are held together by strong electrostatic forces.
6. There are empty spaces between the particles of matter that are very large compared to the particles themselves.

The solid state

In the solid state, the particles are so closely packed (see figure bellow. The particles are held together by strong forces of attraction that act like a chemical glue. Free movement of particles cannot take place. They cannot move around freely in this arrangement. Instead, they vibrate about a fixed position. They are arranged in a fixed pattern which form a cluster of vibrating masses. This makes a solid to have a fixed shape, which cannot be changed except by applying strong external forces.

The liquid state

The particles of a liquid are also closely packed but the forces of attraction between them are weaker than of a solid. These forces of attraction tend to bind them together. The particles have more kinetic energy and they can move around each other. The binding forces are strong when particles come close to one another. It is thought that the particles of a liquid are fairly randomly arranged but consist of "clusters" closely packed together. This property makes a liquid to have a definite volume. However, since the particles are fairly free to move a liquid does not have any characteristic shape (see figure 5.5(b). Thus, a liquid will always take the shape of its container.

The gaseous state

The gaseous state is one in which the particles are moving independently of each other in all directions and at great speeds. The particles of a gas are relatively far apart. They exert no force of attraction on each other. They have more energy than the particles of solids and liquids. They move rapidly and randomly, colliding with each other and with the walls of the container. A typical speed for a molecule of hydrogen in air at ordinary temperature and pressure has been found to be approximately 500 ms^-1

It has been estimated that a nitrogen molecule makes collisions each second. Thus, a gas will rapidly spread out to fill any container in which it is placed. A gas cannot have any shape of its own.

Three states of matter

Physical and chemical changes

Depending on the nature of change, all changes that matter undergoes can be classified as either physical or chemical.

The Characteristics of a Physical Change

Describe the characteristics of a physical change

Physical change

Substances may undergo changes in their physical properties e.g. changes in colour, shape (or form), state, density, structure and texture, etc. If you take a stone and break it down into small particles, you will have only changed its form, but it will remain as a stone. Likewise, melting ice to water or freezing water to ice does not change it, but it is still water. The same case happens when you dissolve salt in water to get a solution of salt in water. You can still get back the original salt by evaporation, except that the crystals of the salt obtained will not look exactly the same as those of the original salt.

These changes of state are examples of physical changes. Physical changes such as melting and boiling do not result in new substances being formed

For example, ice and water still contain the same particles whether in solid (ice) liquid (water) or gaseous (vapour) state.

Changes in states

Characteristics

In the explanation above, we find that in a physical change it is only the physical form, and not the actual nature, of a substance that changes. The changes are brought about by a mere addition or removal of heat, as in the case with water or ice. Such a change is called a physical change. It can be distinguished by the following characteristics:

1. There is no formation of a new substance. Consider an example given above. The ice, liquid water and steam are the solid, liquid and gaseous forms of the same substance (water).
2. There is no change in weight of the substance undergoing the change. If you start with 50g of ice, you will still get the same mass of water and steam (vapour) upon melting and boiling respectively.
3. The changes are readily reversible. You can easily change water back to ice and vapour to water by a mere subtraction of heat (cooling).
4. It is not accompanied by a great heat change. Just a little heat is required to change ice to water, and water to steam.

Physical Changes of Matter Experimentally

Demonstrate physical changes of matter experimentally

Experiment

1. Add some common salt (sodium chloride) to distilled water in a beaker. Stir the mixture until the salt disappears and forms a solution with water. Transfer the water into a porcelain dish. Heat the content until all the water has evaporated off. The salt reappears in its original white solid form.
2. Grind some roll sulphur in a mortar to powder. Put the resultant powder in a test-tube and heat gently, shaking all the time. The sulphur melts to an amber-coloured liquid. On cooling, this liquid returns to its original condition as a yellow solid.
3. Put a block of ice in a beaker. Heat gently until the whole block melts to form water. Pour the water formed in a cup and place it in a deep freezer overnight. The water will freeze back to ice.

You will have seen that all the above changes involve only changes in physical forms of the substances. The chemical nature of substances remained unchanged. Therefore, we can define a physical change as a change that does not involve formation of a new substance but involves a change in state or physical form of the substance and that such a form can be reversed.

The Characteristics of a Chemical Change

Describe the characteristics of a chemical change

Chemical change

Some changes that materials undergo are permanent. Such changes usually involve changes in chemical properties of a substance. For example, when you burn a piece of wood in fire, you get ash. The properties of wood and ash are very different. There is no way you can change ash back to wood. It is practically impossible. A permanent change in chemical properties of a substance is called a chemical change. In a chemical change, a substance losses all its physical and chemical properties.

Characteristics

Includes

1. A chemical change results in the formation of a new substance. The new substance has different chemical and physical properties as compared to the original substance.
2. It is generally not reversible. For example, you cannot turn the ash back to wood.
3. There is a change in weight or mass of the substance undergoing the change. When you burn wood weighing 5 kg, you cannot expect to get the same weight of ash.
4. The change is accompanied by a considerable heat change. For wood to burn to ash a lot of heat must be supplied.

Chemical Changes of Matter Experimentally

Demonstrate chemical changes of matter experimentally

Experiment

1. Strongly heat some roll sulphur on a deflagrating spoon until it melts and begins to burn with a blue flame. If you continue heating, it gradually decreases in amount and finally the spoon will be left empty. The disappearance of sulphur is due to the formation of a new gaseous substance that is invisible. The presence and existence of a gas in air can be defected by its irritating smell. The gas can also be detected by burning the sulphur in a gas jar to which some blue litmus solution has been added. The gas formed, sulphur dioxide, will turn the blue litmus paper into a red one.
2. With the aid of tongs, subject a piece of magnesium ribbon to a Bunsen burner flame. The ribbon burns to produce a new substance, white ash of magnesium oxide.
3. Wrap a wet cotton wool around an iron nail. Keep it in a test tube for 3 days. By the 3^rd day, some brown marks of rust will appear on the surface of the nail. Rust is hydrated iron (III) oxide. This is quite a new substance compared to iron nails.

Table

Differences between physical and chemical changes

Physical change	Chemical change
1. Produces no new kind of matter	Always produces a new kind of matter
2. There is no change is mass or weight of the substance	2. There is a substantial change in the weight of the substance
3. The change can be reversed	3. The change cannot be reversed
4. Little heat is absorbed or evolved	4. Heat changes may be large
5. The change involves only a change in physical properties of a substance	5. Both physical and chemical properties are changed.

Elements and symbols

Depending on the nature of change, all changes that matter undergoes can be classified as either physical or chemical.

The Characteristics of a Physical Change

Describe the characteristics of a physical change

Physical change

Substances may undergo changes in their physical properties e.g. changes in colour, shape (or form), state, density, structure and texture, etc. If you take a stone and break it down into small particles, you will have only changed its form, but it will remain as a stone. Likewise, melting ice to water or freezing water to ice does not change it, but it is still water. The same case happens when you dissolve salt in water to get a solution of salt in water. You can still get back the original salt by evaporation, except that the crystals of the salt obtained will not look exactly the same as those of the original salt.

These changes of state are examples of physical changes. Physical changes such as melting and boiling do not result in new substances being formed

For example, ice and water still contain the same particles whether in solid (ice) liquid (water) or gaseous (vapour) state.

Changes in states

Characteristics

In the explanation above, we find that in a physical change it is only the physical form, and not the actual nature, of a substance that changes. The changes are brought about by a mere addition or removal of heat, as in the case with water or ice. Such a change is called a physical change. It can be distinguished by the following characteristics:

1. There is no formation of a new substance. Consider an example given above. The ice, liquid water and steam are the solid, liquid and gaseous forms of the same substance (water).
2. There is no change in weight of the substance undergoing the change. If you start with 50g of ice, you will still get the same mass of water and steam (vapour) upon melting and boiling respectively.
3. The changes are readily reversible. You can easily change water back to ice and vapour to water by a mere subtraction of heat (cooling).
4. It is not accompanied by a great heat change. Just a little heat is required to change ice to water, and water to steam.

Physical Changes of Matter Experimentally

Demonstrate physical changes of matter experimentally

Experiment

1. Add some common salt (sodium chloride) to distilled water in a beaker. Stir the mixture until the salt disappears and forms a solution with water. Transfer the water into a porcelain dish. Heat the content until all the water has evaporated off. The salt reappears in its original white solid form.
2. Grind some roll sulphur in a mortar to powder. Put the resultant powder in a test-tube and heat gently, shaking all the time. The sulphur melts to an amber-coloured liquid. On cooling, this liquid returns to its original condition as a yellow solid.
3. Put a block of ice in a beaker. Heat gently until the whole block melts to form water. Pour the water formed in a cup and place it in a deep freezer overnight. The water will freeze back to ice.

You will have seen that all the above changes involve only changes in physical forms of the substances. The chemical nature of substances remained unchanged. Therefore, we can define a physical change as a change that does not involve formation of a new substance but involves a change in state or physical form of the substance and that such a form can be reversed.

The Characteristics of a Chemical Change

Describe the characteristics of a chemical change

Chemical change

Some changes that materials undergo are permanent. Such changes usually involve changes in chemical properties of a substance. For example, when you burn a piece of wood in fire, you get ash. The properties of wood and ash are very different. There is no way you can change ash back to wood. It is practically impossible. A permanent change in chemical properties of a substance is called a chemical change. In a chemical change, a substance losses all its physical and chemical properties.

Characteristics

Includes

1. A chemical change results in the formation of a new substance. The new substance has different chemical and physical properties as compared to the original substance.
2. It is generally not reversible. For example, you cannot turn the ash back to wood.
3. There is a change in weight or mass of the substance undergoing the change. When you burn wood weighing 5 kg, you cannot expect to get the same weight of ash.
4. The change is accompanied by a considerable heat change. For wood to burn to ash a lot of heat must be supplied.

Chemical Changes of Matter Experimentally

Demonstrate chemical changes of matter experimentally

Experiment

1. Strongly heat some roll sulphur on a deflagrating spoon until it melts and begins to burn with a blue flame. If you continue heating, it gradually decreases in amount and finally the spoon will be left empty. The disappearance of sulphur is due to the formation of a new gaseous substance that is invisible. The presence and existence of a gas in air can be defected by its irritating smell. The gas can also be detected by burning the sulphur in a gas jar to which some blue litmus solution has been added. The gas formed, sulphur dioxide, will turn the blue litmus paper into a red one.
2. With the aid of tongs, subject a piece of magnesium ribbon to a Bunsen burner flame. The ribbon burns to produce a new substance, white ash of magnesium oxide.
3. Wrap a wet cotton wool around an iron nail. Keep it in a test tube for 3 days. By the 3^rd day, some brown marks of rust will appear on the surface of the nail. Rust is hydrated iron (III) oxide. This is quite a new substance compared to iron nails.

Table

Differences between physical and chemical changes

Physical change	Chemical change
1. Produces no new kind of matter	Always produces a new kind of matter
2. There is no change is mass or weight of the substance	2. There is a substantial change in the weight of the substance
3. The change can be reversed	3. The change cannot be reversed
4. Little heat is absorbed or evolved	4. Heat changes may be large
5. The change involves only a change in physical properties of a substance	5. Both physical and chemical properties are changed.

Compounds and mixtures

Compounds and Mixtures

Concept of compounds and mixtures

A compound is a substance that contains two or more elements chemically combined together. A mixture is something that contains two or more elements not combined chemically. It is always difficult to identify a mixture from a compound. Before going any further into this topic, let us start by looking at the differences between compounds and mixtures. These differences are summarized in the table below.

Differences between mixtures and compounds

Mixtures	Compounds
1. The components of a mixture can be separated by physical means, e.g. filtering, magnetic separation, decantation, etc	The components of a compound can be separated by chemical means only
2. The composition of a mixture can vary widely, e.g. a mixture of 20g of sand with 1g of salt or vice versa.	Compounds are fixed in their compositions by mass of elements present, e.g. there are always 2 atoms of hydrogen to 1 atom of oxygen in a molecule of water
3. Mixing is not usually accompanied by external effects such as explosion, evolution of heat, or volume change (for gases)	Chemical combination is usually accompanied by one or more of these effects
4. Properties of a mixture are the sum of the properties of the individual constituents of the mixture.	The properties of a compound are quite different from those of its constituent elements. For example, water is a liquid whereas its constituent elements, hydrogen and oxygen, are both gases.
5. No new substance is produced as the mixture forms	A new substance is always produced when a compound forms.

A Binary Compound

Prepare a binary compound

A compound is a substance that contains two or more elements chemically combined together. This is a very important difference from mixtures. Mixtures can contain more than one element but the elements are not chemically combined. The number of chemical substances known is approximately four millions. All compounds on earth are made from about one hundred simple materials. Such compounds range from simplest substances, like water, which contains only two elements, to those complex materials of which our own bodily tissues are composed. The following is a short list of common compounds and the elements they are made of.

The Properties of a Compound with those of its Constituent Elements

Compare the properties of a compound with those of its constituent elements

Elemental composition of some compounds

Compound	Constituent elements
Water	hydrogen and oxygen
Carbon dioxide	carbon and oxygen
Ethanol	carbon, hydrogen and oxygen
Sugar (sucrose)	oxygen, hydrogen and carbon
Sodium chloride(common salt)	sodium and chlorine
Marble (calcium carbonate)	calcium, carbon and oxygen
Sulphuric acid	hydrogen, sulphur and oxygen
Sand	silicon and oxygen
Clay	aluminium, oxygen and hydrogen

Compounds have different properties from the elements that make them up. For example:

1. Water (H₂O) is a colourless liquid at room temperature but the elements that make it, hydrogen and oxygen are both gases.
2. Sodium chloride is a white solid made of sodium and chlorine. Sodium is a solid, highly reactive metal, and chlorine is a greenish yellow gas with a chocking smell.

The Concept of a Mixture

Explain the concept of a mixture

A mixture is something that contains two or more substances not combined chemically. The substances may mix up completely or they may remain separate.

Our environment is a mixture of all forms of matter. For example, the earth's crust is a mixture of soils, rocks, minerals, and water. Sea, river, and lake waters contain dissolved gases, living organisms and, sometimes, salt. Air consists of gases, water vapour, and dust particles. The components of each of these mixtures could be elements such as oxygen, nitrogen, sulphur or gold. Alternatively, the mixture might consist of elements and compounds such as hydrocarbons (e.g. petroleum), water, metallic oxides or salts.

Other substances that can form mixtures when placed or mixed together include sand and sugar, maize and bean seeds, soil and table salt, water and mud, etc.

Mixtures into Solutions, Suspensions and Emulsions

Classify mixtures into solutions, suspensions and emulsions

Classification of mixtures

Mixtures can be classified as solutions, suspensions or emulsions. This classification is based on whether the mixed substances dissolve completely or not. It also depends on the nature of the mixtures that result upon mixing. Let us look at each category in detail.

Solutions

A solution is a uniform mixture of two or more substances. Such mixtures may be a solid in a liquid, a liquid in a liquid, a liquid in a gas and, very rarely, a gas in a gas. (See table bellow). We most often think of a solution as being made of a solid dissolved in a liquid. For example, solutions of sugar or salt in water are quite common. A solid that dissolves in a liquid is called a solute while the liquid in which that solid dissolves is called a solvent. For example, sugar and salt are solutes and water is a solvent.

However, other substances that are not normally solids can be found dissolved in a liquid. For example, the gases, carbon dioxide and oxygen, dissolved in water are important for life to continue in oceans, seas, lakes, rivers, etc.

Less obvious perhaps, but quite common, are solutions of one liquid in another. Alcohol mixes (dissolves) completely with water. Beer, wine and whisky do not separate into layers of alcohol and water (even when the alcohol content is quite high). Alcohol and water are completely miscible, that, is they make a solution.

Solutions of gases in gases are very uncommon. Technically, air could be described as a solution of several gases in nitrogen, though this could be unusual everyday use of the term. However, it is interesting to note that different gases always mix completely with each other.

Examples of types of solutions

		Solutes
		Solid	Liquid	Gas
Solvents	Gas	Naphthalene slowly sublimes in air to form a solution	Water vapour in air	Oxygen and other gases in the air
	Liquid	Sucrose (sugar) in water and salt in water	Ethanol (alcohol) in water and various hydrocarbons in each other (petroleum)	Carbon dioxide in water (carbonated water)
	Solid	Steel and other metal alloys	Mercury in gold and hexane in paraffin wax	Hydrogen in metals

Suspensions

A suspension is a cloudy mixture of solid particles suspended in a liquid. A solid is said to be in suspension in a liquid when small particles of it are contained in a liquid, but are not dissolved in it. If the mixture is left undisturbed, the solid particles will slowly settle to the bottom of the containing vessel, leaving the pure liquid above them.

Muddy water is a typical suspension. The mud would settle after a time if left undisturbed leaving brown residue on the bottom of the containing vessel and clear water above. The particles of mud would be retained by filtering whilst the water (and any solids in solution) would pass through.

If you mix flour or chalk dust in water, it forms a suspension. Their particles are simply dispersed (spread) throughout the water and would eventually settle down to the bottom of the vessel if left undisturbed for sometime.

Differences between solutions and suspensions

Solutions	Suspensions
Homogeneous	Heterogeneous
Transparent/clear	Opaque/not clear
Particles completely dissolved	Particles separate on standing
Components separated by evaporation	Components separated by filtration

Emulsions

An emulsion is a cloudy mixture of tiny droplets of one liquid suspended in another liquid. Sometimes two immiscible liquids will not separate out into two layers when mixed together. One of the liquid may form droplets and spread throughout the other to form an emulsion. Cooking oil and water do not mix but they will form an emulsion when they are mixed and shaken. Droplets of oil will spread throughout the water. Unlike pure liquids, emulsions are cloudy (opaque). So you cannot see through them. The emulsion will not settle like a suspension. Which other liquids you know can form suspensions?

Formation of mixtures

Mixtures can be formed from different substances in two major ways.

The first type constitutes homogenous mixtures, where the substances are totally mixed together uniformly. Examples include solutions of salts and sugars in water.

The second type constitutes heterogeneous mixtures, where the substances remain separate and one substance is spread throughout the other as small particles, droplets, or bubbles. All emulsions and suspensions fall under this category. Examples include suspensions of insoluble solids or oil droplets in water.

Separation of mixtures

To make use of the materials around us, we need methods for physically separating the many and varied mixtures that we come across. One of the distinctive characteristics of a mixture of substances is that it is usually possible to separate the constituents by physical means. There are many different physical methods used to separate a wide variety of mixtures. The particular method employed to separate any given mixture depends upon the nature of its constituents. The following are some of the methods in wide use.

The Different Methods of Separating Mixtures

Describe the different methods of separating mixtures

1. Filtration

This method is best applicable in separation of components of mixtures called suspensions.

A mixture of chalk dust or flour with water can be separated by filtering the suspension. The suspended particles get trapped in the filter paper. The trapped particles are called the residue. The water is called the filtrate

Filtration

2. Decantation

This is another method that can be used to separate mixtures called suspensions. However, in this case, separation will be successful if the suspended particles are large enough. Otherwise, the decantation exercise should be accompanied by filtration if you want to get a clear liquid.

Once the solid has settled to the bottom of the container (sedimented), the liquid can be carefully poured off. This is called decantation. Decantation can be applied to separate such components as mixtures of mud, sand or gravel in water and so on.

Decantation of muddy water

3. Evaporation

This method is used to separate substances that form a solution. In such a mixture, the solute is completely dissolved in a solvent to make a uniform solution. To separate these substances, the solution is heated so that the solvent evaporates, leaving the solid residue behind.

A mixture of salt or sugar in water can be separated by applying this method.

Evaporating the solvent

4. Simple distillation

Separating a liquid from a solution can be carried out by distillation. The boiling point of a liquid is usually very much lower than that of the dissolved solid. The liquid can easily be evaporated off in a distillation flask. It is condensed by passing it down a water-cooled condenser and then collected as the distillate

This method can be used to obtain pure water from impure water or from water with dissolved impurities. The process may be used to separate a liquid from a solution or to separate two liquids whose boiling points differ by an appreciable temperature interval. This is a way of getting a pure solvent out of a solution.

Simple distillation

5. Fractional distillation

Separating the liquids from a mixture of two (or more) miscible liquids is again based on the fact that liquids will have different boiling points. However, the boiling points are closer together than for solid-in-liquid solutions. It is difficult to separate mixtures of liquids whose boiling points differ by only a few degrees. In this case, fractional distillation is used.

For example, ethanol boils at 78°C whereas water boils at 100°C. When a solution of ethanol and water is heated, ethanol and water vapours enters the fractionating column. Evaporation and condensation take place as the vapours rise up the column. Ethanol passes through the condenser first as the temperature of the column is raised above the boiling point. Water condenses in the column and flows back into the flask because the temperature of the column is below its boiling point of 100°C.

The temperature on the thermometer stays at 78°C until the ethanol has distilled over. Eventually, the thermometer reading rises above 78C°. This is a sign that all the ethanol has been separated, so heating can be stopped. By watching the temperature carefully, the two liquids (fractions) can be collected separately.

Various forms of fractionating column can be used. Their general purpose is to provide surfaces, e.g. flat discs, on which ascending vapour can condense. Glass beads in the column provide a large surface area for condensation.

Fractional distillation

6. Sublimation

This is a technique used to separate a mixture of solids where one of the solids sublimes. Examples of solids which sublime are ammonium chloride, iodine, solid carbon dioxide and naphthalene. A mixture of any of these solids with another solid can be separated by sublimation.

Let us consider a mixture of iodine and sodium chloride. The mixture is placed in a beaker and covered with a filter funnel as shown in the diagram below. Then, as the mixture is heated, the ammonium chloride sublimes. The ammonium chloride vapour rises and condenses on the cooler walls of the filter funnel. The sodium chloride is left in the beaker.

Sublimation of ammonium chloride

7. Chromatography

This method is commonly used to separate a mixture of coloured substances (solids or dyes). An example of this is the separation of dyes that make up black ink. Chromatography works better when a solvent is used. The commonest solvent is water, though other solvents such as ethanol or ether may be used for those substances that do not dissolve in water. There are two types of chromatography, namely column chromatography and paper chromatography. The two types of chromatography follow the same principle, but paper chromatography is the simplest form to set up, and hence is more commonly used. On which principle does chromatography work? Let us consider an example of separating dyes that make up black ink. In this case, water is used as a solvent.

Separating dyes in ink

Procedure

1. Put a small spot of the water-soluble ink onto a strip of filter paper as shown in figure bellow
2. Place the filter paper in a beaker of water. Make sure the level of the water is below the level of the ink spot.
3. Leave the filter paper until the water has risen to the top of the paper.
4. Remove the paper and allow it to dry.
5. Note the colours the ink contains.

Observation

Separating the components of black ink by paper chromatography

As the solvent (water) moves up the paper, the dyes are carried with it and begin to separate. They separate because they have different solubilities in water and are absorbed to different degrees by the filter (chromatography) paper. As they rise, they are gradually separated.

Findings

The different colours of the ink make a pattern of colours formed during the process of chromatography. This pattern of colours is called a chromatogram.

Figure aboveshows a chromatogram of black ink. The blue ink has the fastest speed. This means it is the most soluble in water and least absorbed by the paper. The green ink has travelled least. This means it is the least soluble in water and most absorbed by the paper.

Paper chromatography showing the separated components of black ink

Uses of Chromatography

Chromatography is used in many different ways. The following are some of the application of chromatography:

1. It can be used to find out the components of a liquid or solid, or even to identify different substances.
2. It can be used by security agents and medical personnel to analyse blood and urine samples.
3. Causes of pollution in water and in animals that live in water can also be detected using chromatography.
4. In chemistry, chromatography is used to test the purity of substances and in separation of mixtures.

8. Layer separation

Mixtures of two immiscible liquids can be separated with a separating funnel. The mixture is placed in a separating funnel and allowed to stand. The liquids separate into two different layers. The lower denser layer is then "tapped" off at the bottom.

For example, when a mixture of kerosene and water is poured into the funnel, the kerosene floats to the top as shown in figure above. When the tap is opened, the water runs out. The tap is closed again when all water has gone, leaving the kerosene in the funnel.

Separating immiscible liquids

9. Solvent extraction

Solvent extraction, also known as liquid-liquid extraction, refers to the separation of materials of different chemical types and solubilities by selective solvent extraction. That is, some materials are more soluble in one solvent than in another. The method is used to refine petroleum products, chemicals, vegetable oils, and vitamins.

This method is used is to separate a solid from a solution in which there is more than one solid dissolved. An example of this is a water solution of iodine and sodium chloride.

EXPERIMENT:Separating iodine from sodium chloride by solvent extraction.

Method

1. Put the solution into a separating funnel as shown in figure (a).
2. Add ethoxyethane. This forms a layer on top of the solution (b). The ethoxyethane is called the extracting solvent.
3. Stopper the separating funnel and shake well figure (c). The iodine, which is more soluble in the ethoxyethane, passes into the ethoxyethane layer. The sodium chloride remains in the water layer.
4. The water layer is run off into a beaker followed by the ethoxyethane layer into another beaker (Caution: Remove the stopper before opening the tap).
5. The ethoxyethane is then evaporated off by simple distillation. Similarly, the water layer can be evaporated to yield sodium chloride.

The solvent extraction works on two principles:

Separating iodine from sodium chloride by solvent extraction

1. One solid in the solution must be more soluble in the extracting solvent than the other.
2. The extracting solvent must not be miscible with the solvent in which the mixture of solids is dissolved. Neither should it react with it.

10. Centrifugation

A centrifuge is used to separate small amounts of suspension. Centrifugation is used with insoluble solids where the particles are very small and spread throughout the liquid. In centrifugation, test tubes containing suspensions are spun round very fast. The solid gets thrown to the bottom. Here, it is no longer the force of gravity on the solid that causes settling.

Instead, there is a huge centrifugal force acting on the particles due to the high speed spinning of the samples. This causes the solid to be deposited at the bottom of the centrifuge tube.

Separation by centrifugation

After centrifugation, the liquid can be decanted (poured out) from the test tube, or removed with a small pipette.

This makes the solid to be left behind.

The solid after centrifugation

11. Magnetic separation

If the solid mixture contains iron, the iron can be removed using a magnet. This method is used to separate scrap iron from other metals. Magnetic iron ore can be separated from other material in the crushed ore by using an electromagnet. In the process of recycling metals, iron objects can be picked out from other scrap metals using electromagnets.

12. Crystallization

This process involves evaporation but the speed of evaporation is much slower. In principle the salt solution can be left in the evaporating basin for a long period until all the water has evaporated but in practice this takes longer time. The process begins by evaporating away the liquid. However, because the crystals are needed, evaporation is stopped after the solution has been concentrated enough. The concentrated solution is allowed to cool slowly and crystallize. The crystals so formed can be filtered off and dried. A similar process is used to extract salt from the sea. Salty sea water is placed in wide basins and put in the sun. Water evaporates off, leaving the salt crystals in basins.

13. Winnowing or threshing

This is a method used to separate grains from husks or bran. The process makes use of the differences in density of the constituents in the mixture. When the winnower is shaken around, grains, being denser than husks or bran, sink to the bottom of the winnower

The less dense husks or bran moves to the top. They are then blown off the winnower by wind or breath, or sometimes picked by hand and separated from the grains.

Separating thresh from grains by winnowing

The Significance of Separating Different Mixtures

Explain the significance of separating different mixtures

We separate mixtures in order to obtain the mixture constituents and put them into appropriate use. The world around us is made up of mixtures of different substances. These substances are often of little use when they are in the form of a mixture. For this reason, separation of the individual components of mixtures is deemed inevitable.

1. (i) Fractional distillation

Is used industrially to separate the various fractions of crude oil such as natural gas, petrol, kerosene, diesel, lubricating oils, waxes, asphalt and bitumen. All these fractions have a significant use in man’s industrial, domestic and commercial activities. The functions or use of all these fractions is well known to everyone of us. Can you mention the functions of each fraction? You will learn more about these products in organic chemistry section.

(ii) Fractional distillation of liquid air

Separates the air into its component gases. This is important because these components have many uses in our everyday life. Some of these fractions and their functions are summarized below:

Component	Use
Nitrogen	Manufacture of fertilizer
Oxygen	Used in hospitals, steel making, diving and space travel
Argon	Filling light bulbs
Carbon dioxide	Fire extinguishing, used in carbonate drinks, etc.
Helium	Filling airships and water balloons
Krypton and Xenon	Used in photographic flash lamps

2. Filtration and purification of drinking water make use of processes such as decantation, filtration and sometimes distillation. The bottled water we drink is prepared by some or a combination of these processes.

3. In mining, an electromagnet is used to separate magnetic iron ore from other materials in the crushed ore.

4. In the manufacture of ethanol by fermentation in breweries, distillation is used in the final stage to purify ethanol to its purest form (surgical spirit) in which the ethanol is usually sold. Likewise, distillation of fermented starch (8-12% ethanol), yields alcoholic drinks called sprits (whisky, gin, brandy, rum) which contain about 35-40% ethanol.

5. (i) Paper chromatography is very useful in analysis of substances present in a solution. For example, it can tell whether a substance has become contaminated or otherwise. This can be very important, because contamination of food or drinking water, for instance, may be dangerous to our health.

(ii) Chromatography has proved very useful in the analysis of biologically important molecules such as sugars, amino acids, and nucleotide bases. Molecules such as amino acids can be seen if the paper is viewed under ultra- violet light.

(iii) Paper chromatography is the test that can be used to check for the purity of a substance. If the sample is pure, it should only give one spot when run in several different solvents.

6. Other separation methods are also used to check whether purification has been successful. Samples obtained by distillation can be re-distilled. The purity of crystals can be improved by re-crystallisation. A water sample can be tested for amount of dissolved material by evaporating a certain amount of water to dryness. The solid waste can be weighed. This would give the amount of dissolved solid in the water.

The process of purification is of crucial importance in many areas of chemical industry. Medical drugs (pharmaceuticals) must be of highest possible degrees of purity. Any contaminating substances even in very small amounts may have harmful side effects.

7. (i) Separation of cream from whole milk is done by the process of centrifugation. As the milk is spun, the heavier contents are forced down and the lighter cream rises up. After centrifugation, the cream is poured off the top by decantation. This is the initial stage of milk constituent separation, after which other components such as milk proteins (cheese) are separated.

(ii) Centrifugation is applicable in blood analysis, where the solid part of blood is separated from the liquid part by centrifugation. Blood is a suspension containing microscopic blood cells (corpuscles) in a liquid called plasma. If blood is centrifuged in a test tube, the blood cells are flung to the bottom, leaving the liquid plasma on top.

8. Knowledge of separation of two immiscible liquids can be applied in the extraction of metals such as iron from their ores. For example, at the base of the blast furnace, the molten slug forms a separate layer on top of the liquid iron. The two can then be "tapped" off separately. The method is very useful in organic chemistry as part of the process called solvent extraction.

9. Evaporation process is used in the extraction of common salt from seawater whereby the sun evaporates water molecules from salty water, leaving crystals of the salt behind.

10. Layer separation technique is applied in the recovery of liquids from contaminants.

11. Solvent extraction process is applied in the extraction of certain edible oils from seeds, and in the extraction of some metals from sludge mixture.

The Components of Different Mixtures using Different Methods

Separate the components of different mixtures using different methods

Activity 1

Separate the components of different mixtures using different methods.

TOPIC 6: AIR COMBUSTION, RUSTING AND FIRE FIGHTING. 

Composition of air

Air is a mixture of different gases. The gases that make up the air include nitrogen, oxygen, carbon dioxide, noble gases (argon, helium, neon, krypton and xenon) and a little water vapour. Air may also contain traces of impurities such as carbon monoxide (CO), sulphur dioxide (SO₂), hydrogen sulphide (H₂S) and other gases. The presence of these gases in air results in air pollution. Table bellow shows the composition of air by volume. The proportion of water vapour and impurities in air is very variable.

The Gases Present in Air and their Proportions

Name the gases present in air and their proportions

The composition of air is not exactly the same everywhere. It changes slightly from day to day and from place to place. There is more water vapour in the air on a damp day and in air above water bodies such as oceans, seas, lakes, rivers, etc. Over busy cities and industrial areas there is more carbon dioxide. But the uneven heating of the earth's surface by the sun causes the air to move continually, resulting in winds. The resultant winds spread the pollutants around.

The percentage composition of air by volume

Gas	Approximate percentage
Nitrogen	78.00%
Oxygen	21.00%
Noble (rare) gases mainly argon	0.94%
Carbon dioxide	0.03%
Water vapour	0 – 4%

The Presence of Different Gases in Air

Demonstrate the presence of different gases in air

The determination of air by mass was carried out by Dumas in 1841. The apparatus used consists of three units as shown bellow.

The three parts of the apparatus include the following:

Determination of the composition of air by weight

1. Several U-tubes containing potassium hydroxide pellets to remove carbon dioxide (only one tube shown in the figure for simplicity).
2. Another set of U-tubes containing concentrated sulphuric acid to remove water vapour (only one tube shown in the figure).
3. A heated, weighed glass tube containing finely divided copper to absorb oxygen.

The three parts of the apparatus would, therefore, remove all carbon dioxide, water vapour and oxygen contained in air. The remaining gas which enters the weighed evacuated flask (globe) will be atmospheric nitrogen and, of course, plus the rare gases. The copper will have reacted with all oxygen to form copper (II) oxide. The increase in mass of the copper will give the mass of oxygen. The increase in weight of the globe will be due to the weight of nitrogen and the rare gases. If we neglect the weight of carbon dioxide, the percentage of oxygen by mass (weight) in dry, pure air is 23.2% and the remaining 76.8% is the percentage of nitrogen and rare gases.

The presence of nitrogen in air

In order to demonstrate the presence of nitrogen in air, we need to carry out an experiment that will convert the nitrogen of the air into a chemically recognizable substance. This is easily done by strongly heating magnesium in the residual gas from the above experiment. Magnesium and nitrogen will react thus:

Upon treatment with water, magnesium nitrite gives ammonia gas. The gas can be recognized by its characteristic smell and its action of turning red litmus paper to blue.

The presence of oxygen in air

Oxygen is known as the active portion of the air because it supports combustion and combines with many other substances. Its presence and composition in air can be determined by using these properties. Any of the following two (2) experiments can be used to determine the composition, by volume of oxygen contained in air.

The Percentage of Oxygen in Air Experimentally

Determine the percentage of oxygen in air experimentally

1. Experiment. Determination of the presence and proportion of oxygen in air by combustion of a candle

Method

1. Place a small candle on a plastic lid or any object that can float. Then set up the apparatus as shown in figure bellow. Sodium hydroxide is used in order to absorb the carbon dioxide gas produced by a burning candle.
2. Light the candle and place the measuring cylinder over the top. Note the level of sodium hydroxide solution in the measuring cylinder at the start. A candle will stop burning (go off) once all the oxygen in the cylinder is used up.
3. When the candle goes off, leave the apparatus to cool to room temperature. The purpose of cooling is to let the heated and expanded air to return to its normal condition. Then note the level of sodium hydroxide solution in the measuring cylinder.

.

Determining the presence and percentage composition of oxygen in air by burning a candle

Observation and findings

The oxygen in air enclosed in the measuring cylinder is used to burn the candle to produce carbon dioxide gas. The carbon dioxide so produced dissolves in sodium hydroxide solution. The dissolved carbon dioxide causes the level of sodium hydroxide solution to rise up. The oxygen gas used to burn the candle is practically equal to the amount of carbon dioxide produced. This fact is, therefore, used to calculate the percentage of oxygen in air.

Model results

In the experiment, the initial volume of air was found to be 70.5 cm³ and the final volume was 55 cm³. The percentage of oxygen in the air is calculated in two steps:

1. To find the volume of oxygen used up to burn the candle (which is practically equal to the volume of carbon dioxide produced and then absorbed by sodium hydroxide), we subtract the final volume of air from the initial volume

Volume or oxygen used = Initial volume of air – final volume of air

Therefore, the volume of oxygen used for combustion of the candle = 14.7 cm.

Alternatively, the volume of oxygen used up can be calculated by subtracting the initial volume of sodium hydroxide solution from the final volume. That is: Volume of oxygen used = final volume of sodium hydroxide – initial volume of sodium hydroxide = Volume of carbon dioxide dissolved in sodium hydroxide.

Therefore, the percentage of oxygen =

In practice, it is difficult to get an accurate result with the above experiment.

This is due to a number of reasons such as:

1. Not all the carbon dioxide is absorbed by the sodium hydroxide.
2. The candle may go out (stop burning) before all the oxygen is used up due to accumulation of carbon dioxide in the cylinder.
3. The heating of the air inside the measuring cylinder causes the gases to expand. This is why it is essential that the gases be allowed to cool to room temperature before reading the level.

Experiment withcombustion of copper in airgives the more accurate results than the combustion of the candle. The copper reacts with oxygen in the air to give copper (II) oxide.

2. Experiment . Determination of the presence and proportion of oxygen in air by the combustion of copper in air

Method

1. Set up the apparatus as shown in figure bellow. Syringe A should contain 100 cm of air, syringe B should be empty.
2. Heat the copper strongly and pass the air from syringe A back and forth (by pushing the piston of the syringe inward and outward) over the copper turnings a few times. Allow the air to cool and measure the volume of air in syringe A.
3. Repeat the heating and cooling until the volume of air that remains in syringe A is constant. The copper is heated and cooled several times to ensure that it reacts with all oxygen in the sample of air.

`

Determining the presence and percentage composition of oxygen in air by heating copper

Observations and findings

2. The final volume of air in the syringe, at the end of the experiment, is less than that of the original volume. This is because oxygen in the original air has combined with copper

Model of result

The volume of air in the syringe at different heating and cooling is as shown below:

Initial volume before heating = 100

Volume after first heating and cooling = 82

Volume after third heating and cooling = 79

The volume of oxygen used up = Initial volume of air before cooling - volume of air after the last heating and cooling

= 100 - 79

= 21

The presence of carbon dioxide in air

Carbon dioxide is present in air to the extent of 0.03% by volume. The gas is formed during the combustion of all common fuels – wood, coal, coke, natural gas, petrol, diesel, paraffin oil, etc, all of which contain carbon.

It is breathed out as a waste product of respiration by all animals. All sorts of combustion and burning produce carbon dioxide. The gas produced by all these processes accumulates in air. However, the amount of carbon dioxide in air remains constant instead of the tremendous quantities released into the atmosphere. This is because plants take up carbon dioxide. They then convert it into complex starchy compounds during photosynthesis. The gas also dissolves in ocean water and other water bodies.

The presence of carbon dioxide in air can be shown by passing air through a test tube containing some limewater (figure 6.5). After a time, the limewater turns milky. This shows the presence of carbon dioxide.

The reaction involved is as follows:

``

Testing for the presence of carbon dioxide in air

The presence of water vapour in air

Water vapour is present in air in varying quantities. It is given off by evaporation from the oceans, lakes and rivers. The presence of water vapour in air can be demonstrated by exposing deliquescent substances to the air on a watch glass. These are substances which when exposed to air tend to absorb much moisture from the air, dissolve in that moisture, and finally form a solution. Examples of deliquescent substances include calcium chloride, sodium hydroxide and phosphorous pentoxide.

The resulting solution is distilled. The colourless liquid obtained from distillation may be proved to be water by various water tests such as use of cobalt chloride paper or anhydrous copper (II) sulphate. The cobalt chloride paper turns from blue to pink in the presence of water. The white anhydrous copper (II) sulphate turns blue. Any of the two tests confirms the presence of water.

Alternatively, one may expose the anhydrous copper (II) sulphate salt to open air straight away for quite some time and then observe any change in its colour and/or form. Upon absorption of water vapour from the air, the white, powdery and anhydrous copper sulphate salt turns into hydrated blue crystals.

The noble (rare) gases

About 1% of the air by volume is made up of the noble gases. The most abundant of the noble gases is argon. Others are neon, xenon, krypton and helium. The proportion of these four is very minute. Argon and neon are used in “gas-filled” electric light bulbs and coloured “neon” electrical signs. They are obtained from liquefied air.

Air pollutants

The air always contains small quantities of many gases. Such gases include hydrogen sulphide, sulphur dioxide, as well as dust and other solid particles, especially in industrial areas. These gases are given off during the combustion of coal, and the fuels resulting from coal.

SEPARATION OF AIR INTO ITS CONSTITUENT GASES

The air we breathe is necessary to keep us alive. It is also a chemical resource. Oxygen is used in steel making, and nitrogen is used in making fertilizers. To use these gases in this way, they must be separated from the atmospheric air. Air, as we studied in chapter 5, is a mixture of different gases. The method used to separate its constituent gases is fractional distillation. The gases have to be liquefied so that the mixture can be fractionally distilled.

The process of separating the air into its constituent gases is difficult. It cannot be done in the laboratory. It is only done in industry. The chemical industry needs the gases from the air in their pure form.

The fractional distillation of air involves essentially two stages:

1. First, the air must be cooled until it turns into a liquid.
2. Then, the liquid air is allowed to warm up again. The various gases boil off at different temperatures

Stage 1: Liquefaction of air

• Air is filtered to remove any dust particles (purification).
• The air is cooled to -180°C to remove the water vapour and carbon dioxide.
• The air is then compressed to 100-150 atmospheres. As the compressed air gets very hot, it has to be cooled.
• The compressed cooled air is allowed to expand rapidly. The rapid expansion cools the air to very low temperatures, and the liquid drops out. At -200°C, only helium and neon remain as gases. The cold gases are used to cool the compressed air.

Stage 2: Fractional distillation of liquid air

The air is cooled and compressed to form liquid air. The liquid air is allowed to warm up. Nitrogen boils off first because it has a low boiling point, -196°C. Argon follows by boiling at -186°C and finally oxygen at -183°C

Figure above illustrates all the steps that take place during the process.

Fractional distillation of liquid air

Combustion

The Concept of Combustion

Explain the concept of combustion

Combustion of a substance in oxygen or air is so common that it becomes almost a habit to use the word "combustion" as if it referred to this kind of reaction alone. In real sense, it may be applied to any chemical reaction accompanied by light and heat in which one or more of the reactants are gaseous.

Many common substances burn in air. Substances such as coal, wood, kerosene, petrol, etc, burn in air. Any substance that burns is called a combustible material. The air or oxygen that supports the combustion is called a supporter of combustion. This is because we live in an atmosphere of air that contains oxygen, which is a very reactive gas. The gas surrounds any burning material. Oxygen is regarded as a supporter of combustion. However, it can sometimes combine chemically with the burning substance to produce a new substance, as we shall see later.

Combustion of a substance involves its reaction with oxygen and the release of energy. These reactions are exothermic and often produce a flame. An exothermic reaction is the one that is accompanied by release of heat to the surrounding environment. Combustion in which a flame is produced is described as burning. During burning energy is given out in the form of heat, light and sound.

The Combustion of Different Substances in Air and Analyse the Products

Demonstrate the combustion of different substances in air and analyse the products

Many different substances burn in air to produce different products. Here are examples of combustion of some common substances:

Sulphur

This is a yellow powder. When burnt in air, it gives misty fumes of sulphur dioxide gas.

Copper

When a piece of copper foil in a pair of tongs is held in a Bunsen flame, it becomes red-hot. On cooling, a black layer of some substance is observed. This black substance is copper oxide. The reaction occurs thus:

Magnesium

When one end of a piece of magnesium ribbon in tongs is placed in a Bunsen flame, it burns with a dazzling flame leaving a white ash. This white ash is magnesium oxide.

Hydrocarbons

Candle wax is a hydrocarbon. When it burns in air, the carbon and hydrogen of the wax react with the oxygen of the air to give carbon dioxide and water vapour respectively.

These are substances containing carbon and hydrogen only. The burning of these organic substances produces carbon dioxide and water vapour as the main products. If oxygen supply is low, combustion is incomplete and carbon monoxide may be formed.

Coal

Coal is a solid fuel that will burn in air to give the following products:

The Application of Combustion in Real Life

Describe the application of combustion in real life

1. The combustion of a natural gas is an important source of energy for homes and industry. Natural gas is mainly methane. Its complete combustion produces carbon dioxide and water vapour.

Substances like methane, which undergo combustion readily and give out large amount of energy, are known as fuels.

2. There are some reactions where fuels and other substances burn to produce a flame. These are combustion reactions. There are also other combustion reactions (exothermic) where no flame is evident. The most important of these is the crucial biochemical reaction that releases energy in our body cells called cellular respiration.

Our bodies need energy to make possible the reactions that take place in our cells. These reactions allow us to carry out our everyday activities. We need energy to stay alive. We get this energy from food. During digestion, food is broken down into simpler substances. For example, the carbohydrates in rice, potatoes and bread are broken down to form glucose. The combustion of glucose with oxygen in the cells of our body provides energy.

The reaction is exothermic and is known as cellular respiration.

3. We combust fuels to heat homes and keep ourselves warm, cook our food, and even burn wastes.

4. Combustion of fuels in automobile engines produces power (energy). This energy is supplied to different parts of motor vehicles to make them move from one point to another or carry out some crucial activities such as grinding, pumping, hauling etc. The operation of such machines could be impossible without combustion of fuel that produces energy to make them work.

5. Combustion of fuel in different burners produces heat and light used for different purposes in a chemistry laboratory.

6. Extraction of metals: Moderately reactive metals such as zinc, iron and lead are roasted in a special furnace (kiln) to form oxides. The resulting oxides are then reduced with carbon to get the pure metal. This process of extracting a metal from its ore by heating is called smelting.

7. In metallurgical industry, combustion is used during welding. Welding is the process of joining metals by melting the parts and then using a filler to form a joint. It can be done using different energy sources, including a gas flame.

Fire fighting

Firefighting is the act of extinguishing destructive fires. A fire fighter fights these fires to prevent destruction of life, property and the environment. Firefighting is a highly technical profession that requires training and education in order to become proficient.

Types of Fires According to their Causes

Classify types of fires according to their causes

Before starting to fight the fire, it is important to know the size and type of the fire that you are going to put off. The kind of firefighting material you are going to use will also depend on the type of fire in question. Fires are classified based on the type of burning materials.

1. Class A fires

These are the fires in which the burning materials are ordinary combustible materials such as paper, wood, cardboard, coal, rubber, clothing, furniture and most plastics. Water is the best extinguisher for these fires. However, any other type of extinguisher, except carbon dioxide, may be used.

2. Class B fires

These fires involve flammable liquids such as petrol, kerosene, oil, alcohol, ether, vanishes, etc. For small fires, a fire blanket or sand may be used. If the fire is large, use foam, dry powder or carbon dioxide extinguisher. Water should not be used on class B fires because the burning material, being lighter than water, will just float and spread the fire further.

3. Class C fires

The burning material involves flammable gases e.g. hydrogen, acetylene, coal gas, butane, methane, propane, etc. The best extinguishers to use in fighting against these fires are foam, dry powder or carbon dioxide extinguishers. It is important to turn off the gas supply, and spray water on the gas tank to cool it down.

4. Class D fires

The burning material is a metal. Alkali metals such as sodium or potassium may catch fire when they come in contact with water and oxygen. At high temperatures, many metals react with oxygen vigorously. Fires that involve burning metals should not be extinguished by water. This is because the burning metal can react with water to give hydrogen (another potential fuel). The appropriate extinguisher to use is foam or dry powder extinguisher.

5. Class E fires

These fires involve electrical equipment such as appliances, wiring, circuit breakers and outlets. You may use carbon dioxide or dry powder extinguisher to put off these fires. Never use water as it can conduct electricity and give an electric shock. Also remember to switch off power from the mains.

6. Class F fires

The burning material is cooking oil or fat. A cooking oil fire in the kitchen can be extinguished by covering the pan with a fire blanket or damp cloth. Foam, dry powder or carbon dioxide extinguishers also work by cutting off the air supply to the fire. For large fires, wet chemical extinguishers are recommended.

Different Types of Fire Extinguishers used to Extinguish Different Types of Fire

Identify different types of fire extinguishers used to extinguish different types of fire

Before choosing the best fire extinguishers for fighting different types of fires it is crucial to identify the type of burning materials first, and hence the type of fire such as:

Class A: Solids such as paper, wood, clothing, rubber, etc

Class B: Flammable liquids such as paraffin, petrol, oil, spirit, alcohol, etc.

Class C: Flammable gases such as propane, butane, methane, hydrogen, etc

Class D: Metals such as aluminium, magnesium, titanium, etc

Class E: Fires involving electrical equipment such as appliances, circuit breakers and outlets, etc.

Types of fire extinguisher to use for each type of fire

Water extinguisher

This is the cheapest and most widely used fire extinguisher. It is used for class A fires. It is not suitable for class B (liquid) fires, or where electricity is involved.

Foam extinguisher

This is more expensive than water extinguisher, but more versatile. It is used for classes A and B fires. Foam spray extinguishers are not recommended for fires involving electricity, but are safer than water if mistakenly sprayed onto live electrical apparatus.

Dry powder extinguisher

This is often termed as “multi-purpose” extinguisher, as it can be used on classes A, B and C fires. It is the best for liquid fires (class B). It will also efficiently extinguish class C (gas) fires. However, take care because it can be dangerous to extinguish a gas fire without first isolating the gas supply. Special powders are available for class D fires.

When powder-type extinguishers are used indoors, the powder can obscure vision or damage goods and machinery. It is also very messy.

Carbon dioxide extinguisher

Carbon dioxide is ideal for fires involving electrical apparatus (class E). It will also extinguish class B (liquid) fires. However, the extinguisher has no post-fire security and the fire could re-ignite.

Wet chemical extinguisher

This is a special extinguisher for class F fires. The extinguisher contains potassium salts. The salts not only help to cool down the flames but also form a ‘saponification’ blanket that effectively smothers the flames with thick, soapy foam.

Specialist powder extinguisher

This is a specialist fire extinguisher for use on class D fires (fires on combustible metals such as sodium, potassium, magnesium, lithium, titanium, manganese and aluminium), especially in the form of powder or turnings.

The Components Needed to Start a Fire

State the components needed to start a fire

To extinguish fire, it is necessary to remove one or more of the three components of combustion. Any fire needs a fuel, oxygen (air) and heat to keep it going. Remove any one of them and the fire will go out. These components are as shown in the fire triangle below.

The fire triangle

A fire will continue or start to burn if these components are present:

(i) Fuel: This refers to any combustible material be it solid, liquid or gaseous material provided it can catch fire and burn. You can stop fire by removing the combustible material from the path of fire.

(ii) Oxygen (air): Oxygen supports combustion. A fuel will only burn if there is sufficient supply of oxygen. You can extinguish fire by displacing, or taking away oxygen supply from the fire or by blocking the gas supply to the fire.

(iii) Heat: The temperature should be at the kindling point of that fuel or above it. Every fuel has its own kindling point. Below the kindling point, the fuel will not catch fire. You can put out fire by lowering the temperature below the kindling point of a particular fuel. Water may be used to cool down the fuel. The vapourization of water absorbs the heat; it cools the smoke, air, walls, objects etc, which could be used as further fuel.

Fire Extinguishers According to the Chemicals they Contain

Classify fire extinguishers according to the chemicals they contain

Fire extinguishers are classified according to the type of chemicals they contain

1. Liquid carbon dioxide extinguisher

This extinguisher contains liquid carbon dioxide. The liquid is contained in a metal container. When the safety pin is removed, carbon dioxide evaporates as solid "snow" (carbon dioxide sublimes). The snow settles on the fire and suffocates it.

2. Soda-acid extinguisher

This extinguisher has a metal case containing soda (aqueous sodium carbonate or sodium hydrogen carbonate). In the metal case there is a glass bottle containing a concentrated acid (sulphuric or hydrochloric acid). There is a knob attached to the top of a metal case. Hitting this knob breaks the acid bottle thus bringing the acid and the soda into contact. The two react to give carbon dioxide, e.g.

The gas forms bubbles with the solution, thereby forming foam which is forced out of a jet of the case. The foam is directed to the fire where it covers the burning liquid, excluding all air from reaching the fire.

Some extinguishers are made in such a way that turning them upside down brings the soda and acid into contact and the reaction proceeds as stated above.

Soda-acid fire extinguishers

3. Foam extinguishers

This is different from the soda–acid type in that it contains sodium hydrogen carbonate in the metal case, but instead of the concentrated acid, it contains aluminium sulphate and saponium in the glass bottle. On mixing the three components, carbon dioxide gas is produced. The gas is ejected out as foam. The foam here lasts longer than the foam in the soda–acid extinguisher. The foam so produced also keeps air away from the burning material.

4. Dry chemical extinguisher

This extinguisher uses powdered sodium hydrogen carbonate and a nitrogen gas kept at high pressure. When the gas cartridge is broken using the top cap, the carbon dioxide under pressure propels the powder. The powder forms a layer over the burning material to keep air away.

Table bellow summarizes the types of fire extinguishers, indicating the chemicals they contain and the classes of fire they are suitable or unsuitable for.

Table: Types fire extinguishers and the chemical composition of their extinguishing agents

Type	Chemical composition of agent	Suitable for	Unsuitable for
APW (Air- pressurized water)	Ordinary tap water pressurized with air	Class A	Class B, C, D and E (will spread the flame and make the fire bigger!)
Dry chemical(DC)	Fine sodium bicarbonate powder pressurized with nitrogen	Class A, B, C and E	- Class D- Aircraft and electronics ( corrosive to metals such aluminium)Note: -Though it is safe to use indoors it can obscure vision
CO2	Non-flammable carbon dioxide gas under extreme pressure	Class B, C and E	Class A (leaves a flammable substance on the extinguished material which canre-ignite later )
Halon	Bromochloro-difluoro-methane	Class A and E	Class B and C (least suitable)
Foam	Proteins and fluoro-proteins	Class A and B	Class E
Wet chemical(WC)	Potassium acetate	Class F	Class E
ABC	Mono-ammonium phosphate with a nitrogen carrier	Class A, Class B and C	Electronic equipment (leaves a stick y residue that may be damaging to electrical appliances such as a computer)
Specialist powder (SP)	Powders of NaCl, Cu or graphite under extreme pressure	Class D	Class A, B, C, E and F

Precautions on using fire extinguishers

The following are some safety precautions you have to keep in mind when using fire extinguishers:

1. Keep a reasonable distance from the fire as it may suddenly change direction.
2. Never use a portable extinguisher on people, instead use a fire blanket.
3. Do not test a portable extinguisher to see if it works. It may leak and later fail to work during an emergency.
4. Do not return a used portable extinguisher to the wall. Make sure it is recharged first.
5. When a fire gets out of control, notify the nearest fire brigade.

Extinguishing Small Fires Using the Right Types of Fire Extinguishers

Extinguish small fires using the right types of fire extinguishers

Activity 1

Extinguish small fires using the right types of fire extinguishers

Rusting

The Concept of Rusting

Explain the concept of rusting

Rusting is the name given to the oxidation of iron or steel in damp air. It is also called corrosion. Rust is hydrated iron (III) oxide. It is a soft, crumbly solid and hence weakens the structure of iron and steel. During rusting, iron reacts with oxygen to form brown iron (III) oxide

At the same time the iron (III) oxide reacts with water to form hydrated iron (III) oxide (or rust):

Note: The x in the equation indicates that the number of water molecules in the hydrated iron (III) oxide can vary. So, both oxygen and water are needed to cause rusting of iron.

Rusting is a serious economic problem. Large sums of money are spent each year to replace damaged iron and steel structures, or protecting structures from such damages. Rusting of bridges, corrugated iron sheets on house roofs, containers, articles, etc. require an expenditure of big sums of money as well as labour for replacement. Rust weakens structures such as car bodies, iron railings, and ships’ hulls, and shortens their useful life. Preventing it can cost a lot of money. All efforts must be made to stop iron or steel items from rusting. This can be achieved if we know the conditions necessary for iron to rust.

The Conditions Necessary for Iron to Rust

Demonstrate the conditions necessary for iron to rust

When iron is left in contact with both water and oxygen (or air), it reacts to form hydrated iron (III) oxide. Iron will not rust on exposure to dry air or air-free water (water that has been boiled to expel all dissolved air) only. However, iron will easily and readily rust in water that has dissolved air in it. In figure 6.8, only the iron nail that is in contact with both water and air rusts. Therefore, rusting will only occur in the presence of both water and oxygen. If one of the two conditions is excluded, in one way or another, rusting will not take place at all.

Testing for conditions necessary for iron rusting

Findings

Nails in tube 1 will rust. Nails in tubes 2 and 3 will not rust.

Reasons

In tube 1, nails are in contact with both water and air (oxygen). In tube 2, the water has been boiled to expel the dissolved air. In addition, any air above the water is prevented from dissolving in boiled water by a layer of oil. So, the nails are completely shielded away from air. Therefore, rusting is impossible. In tube 3, nails are in contact with air only. The moisture present in air is absorbed by anhydrous calcium chloride. Any moisture that might have been absorbed by the anhydrous calcium chloride is prevented from reaching the nails by a tuft of cotton wool. The cotton wool also absorbs some moisture directly from the air. Therefore, tube 3 will always carry dry air (moisture-free air). Hence, no rusting of iron nails occurs.

This experiment demonstrates the fact that for iron to rust, both water and air (oxygen) must be present. If one of these conditions is controlled, no rusting can take place.

Similarity between rusting and burning

Chemically, rusting and burning are similar processes in that they both require oxygen. Consider the burning of magnesium to give magnesium oxide.

In this process, magnesium combines with the oxygen of the air to form magnesium oxide.

During rusting, iron combines with oxygen of the air in the presence of water to form brown hydrated iron (III) oxide, "rust."

In addition, the two processes, burning and rusting, are exactly similar in that they both generate heat. The only difference is in the time required for each of the two processes to take place. During rusting heat is given out, but without being noticed because of its slower rate of production. Burning produces noticeable heat and light.

The Different Methods of Preventing Iron from Rustin

Describe the different methods of preventing iron from rusting

We have learned that for iron to rust there must be direct contact between the iron and both water and oxygen from the air. Therefore, in order to stop rusting we must protect iron from either water (moisture) or oxygen (air) or both. The following are some of the methods used to prevent iron from rusting:

Painting

Painting the iron article creates a waterproof and airproof cover over the surface of the iron. This method is widespread for objects ranging in size from ships and bridges to garden gates. Paints that contain lead or zinc are mostly used. These paints are especially good for preventing rusting. For example, "red lead" paints contain an oxide of lead,.

As oxygen and water cannot reach the iron, it does not rust. However, if the paint layer is scratched off rusting may occur. So, regular repainting is necessary to keep this protection intact.

Oiling and greasing

The oiling and/or greasing of the moving parts of machinery forms a protective film, preventing rusting. Moving parts cannot be painted since the paint layer can be easily scratched off during movement. Again, the treatment must be repeated to continue the protection.

Plastic coating

Steel is coated with plastic for use in garden chairs, refrigerators, bicycle baskets, dish racks, etc. The plastic PVC (polyvinyl chloride), a trade name for polychloroethene, is often used for this purpose. Plastic is cheap and can be made to look attractive.

Electroplating

Electroplating is the coating of one metal with a layer of another metal by means of electrolysis, where the metal to be coated is the cathode and the coating metal the anode.

An iron or steel object can be electroplated with a layer of chromium or tin to protect against rusting. A ‘tin can’ is made of steel coated on both sides with a fine layer of tin. Tin is used because it is unreactive and non-toxic. However, if protective layer is broken, then the steel beneath will begin to rust. So, proper handling of tin-plated items is needed.

Galvanizing

An iron object may be covered with a layer of zinc. This is called galvanizing. Even if the zinc is scratched to expose the iron, the iron does not rust. This is because zinc is higher in the reactivity series than iron. So, zinc reacts with water and oxygen in preference to iron.

The zinc layer can be applied by several different methods. These include electroplating or dipping the object into molten zinc. When an iron or steel article is dipped into molten zinc and then removed, it becomes coated with a thin layer of zinc. The zinc forms a protective coat over the surface of iron. This process is used for dustbins, car bodies, barbed wires and motorway crash barriers.

Sacrificial protection

This is a method of rust protection in which blocks of a metal more reactive than iron are attached to the iron surface. Zinc and magnesium are more reactive than iron. When blocks of zinc or magnesium are attached to the hull of a steel ship or oil rig, it corrodes in preference to iron. This is called sacrificial protection because the zinc or magnesium is sacrificed to protect the iron. When the blocks are nearly eaten away, they can be replaced by fresh blocks. Underground gas and water pipes are connected by wire to blocks of magnesium to obtain the same protection.

It is not necessary to cover the whole surface of a steel article with the more reactive metal for sacrificial protection to work. A ship may have magnesium blocks riveted to its hull every few metres to prevent rusting of the whole hull.

Blocks of zinc (or magnesium) attached to the hull of a ship

Alloying

Alloys are mixtures of metals. For example, iron can be mixed with small quantities of much less reactive metals to form an alloy called stainless steel. Stainless steel contains iron mixed with chromium, nickel and manganese. Stainless steel does not rust. It also has a very attractive appearance. It is used to make cutlery and kitchen equipment.

Use of silica gel

Silica is a common name for silicon dioxide (SiO₂). Silica gel is a granular, vitreous, highly porous form of silica made synthetically from sodium silicate. Despite its name, silica gel is a solid. It is used as a desiccant, which absorbs moisture to prevent rusting of iron items or articles. Most often, a small bag of silica gel is put inside bags or boxes used for storing or carrying iron items to absorb any moisture that may cause rusting.

CHEMISTRY FORM ONE ALL TOPICS
CHEMISTRY FORM ONE TOPIC 1 & 2 
CHEMISTRY FORM ONE TOPIC 3 & 4. 
CHEMISTRY FORM ONE TOPIC 5 & 6. 

O'LEVEL CHEMISTRY
CHEMISTRY STUDY NOTES, FORM FOUR. 
CHEMISTRY STUDY NOTES, FORM THREE. 
CHEMISTRY STUDY NOTES, FORM TWO.
CHEMISTRY STUDY NOTES FORM ONE.