COMPOUNDS AND MIXTURES
COMPOUND
Defn. (i) A compound is a pure substance made up of two or more elements in a chemical combination.
OR (ii) A compound is a pure substance which consists of two or more elements which are chemically combined together.
Examples of compounds are Common salts, water, sugar, carbon dioxide, petrol, diesel, alcohol, baking powder etc.
When a compound is made up of two components is referred to as a binary compound. Examples of binary compounds include common salt, carbon dioxide and water.
A binary compound is formed when two or more pure substance of the same or different types are chemically combined together.
Table below shows examples of substances that combine to make binary compounds.
| S/N | FIRST PART | SECOND PART | COMPOUND |
| 1 | Sulphur | Oxygen | Sulphur dioxide |
| 2 | Sodium | Chlorine | Sodium chloride |
| 3 | Hydrogen | Oxygen | Water |
| 4 | Nitrogen | Hydrogen | Ammonia |
| 5 | Zinc | Sulphur | Zinc sulphide |
Characteristics (properties) of binary compounds
(i) Its components can be separated by chemical means only
(ii) Its components are in fixed ratio. (i.e whenever a compound is formed the substance in it combine in a definite proportion.
(iii) Its formation involves only chemical change (reaction).
(iv) Its properties are quite different from those of its components.
(v) The components cannot be seen separately.
(vi) Its formation involves energy change.
DIFFERENCES BETWEEN ELEMENTS AND COMPOUNDS
| S/N | ELEMENTS | COMPOUNDS |
| 1 | Can not be separated into simpler substances | The components can be separated by chemical means |
| 2 | They are made up of similar atoms of the same type | Can be made up of two or more substances that are naturally different. |
| 3 | They maintain their characteristics when are in mixtures | Have different characteristics from their components when they are made |
4 |
Contain unique atomic number | Have varying total atomic numbers depending on their components. |
| 5 | Symbols represent the elements | Chemical formula represents a compound. |
Elements and compounds are similar in
(i) Element and Compound are both pure substances made from their constituents as
homogenous substances and cannot be separated by physical means.
(ii) Elements and compounds are both made from atoms as their building blocks and their components are mostly combined in fixed ratio.
MIXTURES
Defn. Mixture is a physical combination of two or more substances in any ratio
OR
A mixture is a substance that consists of two or more substances (elements) which are not chemically combined together.
Since mixtures are not chemically combined, they can be separated by physical means. Mixtures can be Liquid – Liquid (eg Oil and water), Solid – Liquid (eg muddy water) or Solid – Solid (eg Sand and salt).
Other examples of mixtures are: Milk, sea water, sugar solution, tea, blood, soda, Air etc
Mixtures can be Homogenous or Heterogeneous.
Homogenous mixture is a mixture which has uniform compositions, appearance and properties.
Eg when salt is dissolved in water every section of the solution is identical in composition, appearance and physical properties,
Other examples of homogenous mixture are tea, air, sugar solution.
Heterogeneous mixture is a mixture which has different compositions, appearance and properties at various point in the mixture.
For example, when sulphur powder and iron fillings are mixed together, they form heterogeneous mixture. A mixture is physically combined and can be separated by a bar magnet
Other examples of heterogeneous mixtures are Sand and water, oil and water, chalk powder and water.
Characteristics of mixtures
(i) Its components can be separated by physical means.
(ii) Its components are not in fixed ratio.
(iii) Its formation involves physical change.
(iv) Its properties are those of its components in it.
(v) The components can be seen separately.
(vi) No energy change when it is formed.
As seen above, mixtures and compounds have different properties.
The table below shows the difference in properties between mixtures and compounds.
| MIXTURE | COMPOUND |
| 1. The components in mixture can be separated
by physical means |
The elements in compound cannot be separated by physical means, (but can be separated by chemical means) |
| 2. The composition of mixture is variable | The composition of compound is fixed |
| 3. No chemical change occurs when mixtures are
formed. |
Chemical change occurs when compounds are formed |
| 4. The properties of the mixture are those of
individual components |
The properties of the compound are very different from those of the individual elements. |
| 5. Components in mixture can be seen separately | Components in compound cannot be seen separately |
| 6. No energy change occurs when it is formed. | Energy change occurs when it is formed. |
EXERCISE
1. You are provided with the following substances: Common salt, mud, juices, milk, water, soft drink,
kerosene, diesel and air. Classify the substances as either compounds or mixtures and give reasons for
your responses.
2. Provide examples of how elements, compounds and mixtures are used in every day life.
SOLUTIONS, SUSPENSIONS AND EMULSIONS
Liquid mixtures can be classified into Solutions, suspensions or emulsions depending on their compositions.
(1) SOLUTION
Defection : Solution is a homogeneous (uniform) mixture of two or more substances which are solvent
and solute
Such mixtures (solution) may be a solid in a liquid, a liquid in a liquid, a liquid in a gas and, and a gas in a gas.
Examples of solutions are, solution of sugar in water and salt in water (LIQUID SOLUTIONS), a solution of zinc in copper (SOLID SOLUTION), Air is a solution of oxygen in nitrogen (GAS SOLUTION). etc
A solution is made up of solvent and solute
Definition: (i) Solvent is a component of the solution that dissolves the solute.
OR (ii) Solvent is a substance that dissolves a solute.
Solvent is a component that is usually present in large amount in a solution. Examples of solvent are: water, alcohol, diesel, petrol, kerosene
Definition (i) Solute is component of the solution that is dissolved in the solvent.
OR (ii) Solute is a substance that dissolves in a solvent
Solute is a component that is usually present in small amount in a solution. Examples of solute are sugar, salt, grease
TYPES OF SOLUTIONS
A solution can either be (i) Unsaturated solution (ii) Saturated solution (iii) Super saturated solution
UNSATURATED SOLUTION
An unsaturated solution is a solution in which solvent can dissolve more solute at a given temperature and pressure.
(Here the solutes completely dissolve, leaving no remaining solutes)
SATURATED SOLUTION
A saturated solution is a solution in which a solvent cannot dissolve more solute at a given temperature and pressure.
(Saturated solution leaves the undissolved solutes at the bottom)
SUPER SATURATED SOLUTION
A super saturated solution is a solution that holds more solute than the maximum amount it can dissolve at a given temperature and pressure.
NB: Saturation depends on temperature. As the temperature increases, the kinetic energy of solvent molecules increases and hence more solute particles dissolve.
APPLICATION OF SATURATION
Saturation is used when
(i) Separating certain mixtures in laboratory
(ii) Extracting some minerals such as extracting common salt from sea water.
(iii) Cooking and salting food
(iv) Using detergents during laundry
(v) Dissolving sugar in tea.
CLASSIFICATION OF SOLUTIONS INTO THREE STATES OF MATTER
Solutions can exist in the three states of matter which are solids, liquids and gases. The solutes and solvents can be in any state, that is solid, liquid or gas.
Table below shows examples of types of solutions in the three states of matter
| SOLUTE | SOLVENT | EXAMPLES |
| SOLID | GAS | Naphthalene slowly sublimes in air to form a solution |
| SOLID | LIQUID | Sugar in water and salt in water |
| SOLID | SOLID | Steel and other metal alloys |
| LIQUID | GAS | Water in air |
| LIQUID | LIQUID | Ethanol (alcohol) in water and various hydrocarbons in each other (petroleum) |
| LIQUID | SOLID | Mercury in gold and hexane in paraffin wax |
| GAS | GAS | Oxygen and other gases in the air |
| GAS | LIQUID | Carbon dioxide in water (carbonated water) |
| GAS | SOLID | Hydrogen in metals |
From the table above, Examples of
SOLID SOLUTION: (i) Steel (solution of carbon, sulphur in iron),
(ii) Brass (solution of zinc in copper)
LIQUID SOLUTION: (i) Alcohol in water
(ii) Vinegar (a solution of acetic acid in water)
GASEOUS SOLUTION: (i) Air (solution of oxygen in other gases in air)
(ii) Water vapour in air
USES OF SOLVENTS
Solvents are used in homes, institutions such as schools and colleges, hotels and in industries.
The following are some of the uses of solvents
(i) Are used in cleaning (because they form a solution with the dirty (solute)
(ii) Are used in varnish removal
(iii) Are used in stain removal
(iv) Are used in bleaching
(v) Are used in thinning paints
(vi) Are used in degreasing
(2) SUSPENSION
Definition. A suspension is heterogeneous mixture of liquid (solvent) and fine particles of solid.
OR
A suspension is heterogeneous mixture in which the solid particles settle to the bottom on standing but spread throughout when shaken.
In suspension the solute particles do not dissolve but get suspended in the liquid. For example, when you add flour into water during cooking you have to keep on stirring, otherwise the flour will settle. This is an example of suspension.
Other examples of suspension include, Paints, porridge, muddy water, chalk powder in water, blood, sand particles suspended in water, some medicine written shake well before use are suspensions.
Suspensions composed of either liquid droplets or fine solid particles suspended in a gas are called Aerosols.
Suspensions are used in many aspects in our daily life and stored in containers labelled shake well before use. Examples of these are medicines (Syrups), Body sprays, some paints, insecticides etc.
DIFFERENCE BETWEEN SOLUTION AND SUSPENSION
| SOLUTION | SUSPENSION |
| 1. It is homogeneous mixture | It is heterogeneous mixture |
| 2. It is transparent (clear) | It is opaque (not clear) |
| 3. Solute particles completely dissolved in solvent | Solute particles settle if the suspension is undisturbed |
| 4. Components are separated by evaporation | Components can be separated by filtration. |
(3) EMULSIONS
Definition: Emulsion is a mixture of liquids that do not completely mix with each other.
An emulsion is usually formed from two liquids, one water -based liquid and the other oil-base liquid. When shaken the oily forms droplets suspended in the water- based liquid. The harder the emulsion is shaken, the smaller the droplets, so the emulsion may appear to be a homogeneous solution
Example of emulsions are Milk, which contains drops of butter fat in water
Emulsion paint, which contains is drops of coloured oils in water
COMPOUNDS AND MIXTURES
MISCIBLE AND IMMISCIBLE LIQUIDS
Miscible liquids are liquids which mix up completely without forming layers. Eg methylated spirit and water, Ethanol and water, benzene and paraffin, water and soda etc
Immiscible liquids are liquids which do not mix up completely i.e they form layer. Eg Kerosene and water, Oil and water, chloroform and water etc.
