Chapter 5-
Exploring Mixtures and their
Separation
1. Crystallization
Type
of mixture used for: Homogeneous mixtures in which
solids are dissolved in liquids.
Principle
of the technique: It is based on the difference in
solubility of substances at different temperatures. On cooling a hot saturated
solution, the dissolved substance separates out as pure crystals.
Importance
of the technique: It is used to obtain pure solids
and remove impurities from substances.
Applications: Preparation of copper sulfate crystals, formation of sugar
crystals (mishri), and salt production from seawater.
2. Distillation
Type
of mixture used for: Homogeneous mixtures of two
miscible liquids or a liquid containing dissolved solids.
Principle
of the technique: It works on the difference in
boiling points of substances (more than 25 °C). The liquid with the lower boiling point vaporises first and is then condensed back into liquid
form.
Importance
of the technique: It helps in recovering pure
liquids and separating solvents from solutions.
Applications: Separation of acetone and water, preparation of perfumes, and
purification of liquids and water.
3. Fractional Distillation
Type
of mixture used for: Mixtures of miscible liquids
having small differences in boiling points.
Principle
of the technique: It involves repeated vaporisation
and condensation to separate liquids into different fractions.
Importance
of the technique: It is an important industrial
method for separating useful fuels and chemicals.
Applications: Separation of crude petroleum into LPG, petrol, diesel, kerosene,
etc.
4. Paper Chromatography
Type
of mixture used for: Homogeneous mixtures
containing coloured substances.
Principle
of the technique: Different components move at
different speeds on paper due to varying interactions with the solvent and
paper.
Importance
of the technique: It helps identify and separate
components present in very small quantities.
Applications: Separation of colours in ink, pigments from leaves and flowers,
and food colour analysis.
5. Separating Funnel
Type
of mixture used for: Heterogeneous mixtures of two
immiscible liquids.
Principle
of the technique: It is based on the difference in
densities of liquids, which form separate layers.
Importance
of the technique: It provides an easy method for separating liquids that do not mix.
Applications: Separation of oil and water and mustard oil from water.
6. Sublimation
Type
of mixture used for: Mixtures containing a
sublimable solid and a non-sublimable substance.
Principle
of the technique: Some solids change directly into
vapour on heating and return directly to solid on cooling.
Importance
of the technique: It is useful for separating
substances without melting them.
Applications: Separation of camphor and sand, purification of naphthalene, and
use of dry ice in storage.
7. Filtration
Type
of mixture used for: Heterogeneous mixtures
containing insoluble solids in liquids.
Principle
of the technique: The filter medium allows liquid
to pass while retaining insoluble solid particles.
Importance
of the technique: It is a simple, effective method for removing larger insoluble impurities.
Applications: Separation of sand from water and filtering saturated solutions
during crystallization.
8. Centrifugation
Type
of mixture used for: Suspensions and colloids
containing solid particles in liquids.
Principle
of the technique: Rapid spinning causes heavier
particles to move outward and settle at the bottom.
Importance
of the technique: It separates very fine particles
quickly and efficiently.
Applications: Separation of blood components, laboratory testing, and medical
diagnosis using the paperfuge.
9. Coagulation
Type
of mixture used for: Suspensions containing very
fine suspended particles.
Principle
of the technique: A coagulant causes tiny particles
to clump together and settle down.
Importance
of the technique: It is important in purification
processes and the treatment of impure water.
Applications: Water purification using alum and preparation of paneer or cheese
from milk.
10. Evaporation
Type
of mixture used for: Solutions containing dissolved
solids.
Principle
of the technique: The liquid solvent evaporates,
leaving behind the dissolved solid.
Importance
of the technique: It is one of the simplest methods
to recover dissolved solids.
Applications: Obtaining salt from seawater.
11. Sedimentation and Decantation
Type
of mixture used for: Suspensions containing heavier
insoluble particles.
Principle
of the technique: Heavier particles settle down due
to gravity, and the clear liquid is carefully poured off.
Importance
of the technique: It is useful for basic
purification and separation of insoluble solids.
Applications: Separation of mud from water and water treatment processes.
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