Mixture :-
A mixture is a substance formed when two or more elements or compounds are physically combined in any proportion, without undergoing a chemical change.
Examples:
Air → mixture of nitrogen, oxygen, carbon dioxide, etc.
Salt solution → mixture of salt and water
Soil → mixture of minerals, sand, clay, organic matter, etc.
Classification of Mixtures:-
Mixtures are mainly classified into two types:
1. Homogeneous Mixture
A homogeneous mixture has a uniform composition throughout. Its components are completely mixed and cannot be distinguished separately.
Examples:
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Salt solution
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Sugar solution
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Air
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Brass (copper + zinc)
Key point: It has only one visible phase.
2. Heterogeneous Mixture
A heterogeneous mixture does not have a uniform composition throughout. Its components can often be distinguished separately.
Examples:
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Sand and water
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Oil and water
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Soil
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Iron filings and sulphur
Key point: It may have two or more visible phases.
Solutions:-
A solution is a homogeneous mixture of two or more substances.
For example, when salt dissolves in water, salt solution is formed.
1. Solute
The substance that gets dissolved in a solution is called the solute.
Example: In salt solution, salt is the solute.
2. Solvent
The substance that dissolves the solute is called the solvent.
Example: In salt solution, water is the solvent.
Remember:
Solute + Solvent → Solution
3. Concentration
The amount of solute present in a given amount of solution is called the concentration of the solution.
Mass percentage=(Mass of solute / Mass of solution)×100
where:
Mass of solution = Mass of solute + Mass of solvent
Example: If 10 g salt is dissolved in 90 g water:
Mass of solution = 10 + 90 = 100 g
Mass percentage of salt:
(10/100) X 100 = 10%
4. Solubility
Solubility is the maximum amount of a solute that can dissolve in a given amount of solvent at a particular temperature to form a saturated solution.
Example: If no more sugar dissolves in water at a particular temperature, the solution has reached its solubility limit.
5. Saturated Solution
A saturated solution is a solution that contains the maximum amount of solute that can dissolve in the solvent at a given temperature.
Example: If you keep adding sugar to water and eventually some sugar remains undissolved at the bottom, the solution is saturated.
Methods of Separation of Homogeneous Mixtures –
Homogeneous mixtures can be separated into their components using different physical methods, depending on the properties of the substances.
1. Crystallization
Crystallization is used to obtain a pure solid substance in the form of crystals from its solution.
Principle: Difference in solubility of the substance at different temperatures.
Example: Obtaining pure copper sulphate crystals from copper sulphate solution.
Basic process:
Solution → Heating/concentration → Cooling → Crystals
Important: Crystallization is generally preferred over simple evaporation when a pure crystalline solid is required.
2. Distillation
Distillation is used to separate a solvent from a solution by using the difference in boiling points.
Principle: Difference in boiling points.
Example: Obtaining pure water from salt solution.
Process:
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Heat the solution.
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The component with the lower boiling point changes into vapour.
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Vapour is cooled in a condenser.
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It changes back into liquid and is collected.
Salt solution → Heating → Water vapour → Cooling → Pure water
3. Fractional Distillation
Fractional distillation is used to separate two or more miscible liquids having close boiling points.
Principle: Difference in boiling points of liquids.
Example: Separation of different components of petroleum and separation of liquid air into nitrogen and oxygen.
A fractionating column is used to make the separation more effective.
Key point:
Distillation → usually liquids with a significant difference in boiling points
Fractional distillation → liquids with close boiling points
4. Paper Chromatography
Paper chromatography is used to separate and identify different components of a mixture based on their different rates of movement through a medium.
Principle: Different components have different solubilities in the solvent and different attractions towards the paper.
Example: Separating different colours present in black ink.
Basic process:
A spot of ink is placed on chromatography paper.
The paper is placed in a suitable solvent.
The solvent moves upward through the paper.
Different dyes move at different speeds.
Separate coloured spots appear.
Methods of Separation for Heterogeneous Mixtures:-
Separating Funnel
A separating funnel is used to separate two immiscible liquids—liquids that do not mix with each other.
Example: Oil and water
Principle-
It works on the basis of difference in density.
The denser liquid settles at the bottom.
The less dense liquid forms the upper layer.
The lower layer can be drained through the tap.
Sublimation
Sublimation is the process in which a solid changes directly into vapour without becoming liquid.
It can be used to separate a sublimable solid from a non-sublimable solid.
Examples:
Ammonium chloride + sand
Iodine + sand
Principle
On heating, the sublimable substance changes directly into vapour. The vapour is then cooled and collected as a solid.
Centrifugation
Centrifugation is a method of separating components of a mixture by rapidly rotating the mixture.
Principle
It works mainly on the basis of difference in density.
During rapid rotation:
Heavier particles move towards the bottom/outside.
Lighter particles remain above.
Examples:
Separating cream from milk.
Separating suspended particles from a liquid.
Coagulation
Coagulation is the process in which very small suspended or colloidal particles come together to form larger particles or lumps, making them easier to separate.
Example: Purification of muddy water
Certain substances such as alum (fitkari) can help suspended particles come together. The larger particles then settle down more easily.
Important
Coagulation itself is not simply a filtration process. It is a pre-treatment that makes suspended particles larger and easier to remove by sedimentation or filtration.
Suspension
A suspension is a heterogeneous mixture in which insoluble solid particles are dispersed in a liquid and are large enough to settle down when left undisturbed.
Examples
Muddy water.
Sand in water.
Properties
1.Particles are large and can often be seen with the naked eye.
2.Particles settle down on standing.
3.They can generally be separated by filtration.
4.They scatter light, so the path of light can be visible.
Colloid
A colloid is a heterogeneous mixture in which very small particles of one substance are dispersed throughout another substance.
Examples
Milk, Fog, Smoke, etc.
Properties
1.Colloidal particles are smaller than suspension particles.
2.They do not normally settle down on standing.
3.They generally cannot be separated by ordinary filtration.
4.They scatter light. This is called the Tyndall effect.
Tyndall Effect
The Tyndall effect is the scattering of light by very small particles present in a colloid or suspension, which makes the path of the light visible.
Simple Example
When a beam of sunlight enters a dusty room through a window, you can see the path of the light because dust particles scatter the light.
Examples
• Sunlight visible through fog.
• A car's headlights visible in fog.
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