Describe appropriate ways to separate the components of different types of mixtures (sorting, evaporation, filtration,
magnets, boiling, chromatography, screening.
Describe how paper chromatography is used to separate the mixtures of ink in a black sharpie pen.
Some of the methods for separation of mixtures are: Sedimentation or Decantation, Filtration,
Evaporation, Chromatography, Crystallization, Sublimation, Magnetic, and Gravity method.
Classification of matter can be summarized as follows:
Because molecules in ink and other mixtures have different characteristics (such as size and
solubility), they travel/migrate at different speeds (distance/time) when pulled along a piece of paper by a
solvent (in this case, alcohol). For example, black ink contains several colors. When the water flows through
the ink, the molecules of each one of the colors behave differently, resulting in a sort of “rainbow” effect.
Chromatography is used to separate mixtures of substances into their components.
All forms of chromatography work on the same principle.
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They all have a stationary phase (a solid, or a liquid supported on a solid: This is the Chromatography paper)
and a mobile phase (a liquid or a gas: This is the alcohol). The mobile phase (alcohol) flows through the
stationary phase (chromatography paper) and the mobile phase carries the components of the mixture (the
ink) with it. Different components or colors of the ink travel at different rates. Look at the different colors and
where they are on the paper.
A mixture is a combination of two or more elements or compounds in any proportion so that the components
do not lose their identity. Air is an example of a mixture (several gases mix to form air).
Mixtures are of two types, homogeneous and heterogeneous.
Homogeneous mixtures have the same composition throughout the sample. The components of such mixtures
cannot be seen under a powerful microscope. They are also called solutions. Examples of homogeneous
mixtures are air, sea-water, gasoline, brass etc.
Heterogeneous mixtures consist of two or more parts (phases), which have different compositions. These
mixtures have visible boundaries of separation between the different constituents and can be seen with the
naked eye e.g., sand and salt, chalk powder in water etc.
Separation of Mixtures
The separation of mixtures into its constituents in a pure state is an important process in chemistry. The
constituents of any mixture can be separated on the basis of their differences in their physical and chemical
properties e.g., particle size, solubility, effect of heat, acidity or basicity etc.
Mixtures
A mixture is a combination of two or more elements or compounds in any proportion so that the
components do not lose their identity. Air is an example of a mixture (several gases mix to form air).
Mixtures are of two types, homogeneous and heterogeneous. Homogeneous mixtures have the
same composition throughout the sample. The components of such mixtures cannot be seen under a
powerful microscope. They are also called solutions. Examples of homogeneous mixtures are air,
sea-water, gasoline, brass etc. Heterogeneous mixtures consist of two or more parts (phases), which
have different compositions. These mixtures have visible boundaries of separation between the
different constituents and can be seen with the naked eye e.g.sand and salt, chalk powder in water
etc.
Separation of Mixtures
The separation of mixtures into its constituents in a pure state is an important process in chemistry.
The constituents of any mixture can be separated on the basis of their differences in their physical
and chemical properties e.g., particle size, solubility, effect of heat, acidity or basicity etc.
Some of the methods for separation of mixtures are Sedimentation or Decantation
AimTo separate the mixture of coarse particles of a solid from a liquid e.g., muddy river water.
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Sedimentation or Decantation
Aim
To separate the mixture of coarse particles of a solid from a liquid e.g., muddy river water.
Experiment
Aim
To separate the mixture of coarse particles of a solid from a liquid e.g., muddy river water.
Principle
The coarse particles of the solid being heavier than the liquid (usually water), settle down due to
gravity. The clear upper layer of the liquid is then gently poured out into another container. Settling
down of the coarse particles due to the effect of gravity is called sedimentation. The mechanical
transfer of the clear upper liquid without disturbing the settled solid particles is called decantation.
Process
The mixture is taken in a container and allowed to stand for sometime. The solid particles settle down
with time. Settling down of the particles leaves the upper layers of the liquid clearer. Bigger particles
settle down faster than the finer particles. Sometimes the sedimentation process is hastened by
adding a small quantity of alum. Al3+ ions in alum cause the coagulation of the fine particles by
undergoing hydrolysis to Al(OH)3 that has a strong tendency for adsorption.
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Fig: 1.1 - Separation of the coarse particles of a solid from a liquid by sedimentation and decantation
Filtration
Aim
To separate the insoluble solid component of a mixture from the liquid completely i.e. separating the
precipitate (solid phase) from any solution.
Experiment
Aim
To separate the insoluble solid component of a mixture from the liquid completely i.e. separating the
precipitate (solid phase) from any solution.
Principle
The solvent molecules and the molecules/ions present in the solution can pass through the porous
membranes while the suspended particles cannot and are retained on the porous membrane.
Process
The solution containing the suspended impurities is made to pass through the porous membrane
such as filter paper, filter cloth etc. The solvent or solution containing dissolved substances passes
through the porous membrane, which is called filtrate. The insoluble solid suspended particles that
remain on the porous membrane is termed residue. When the suspended impurities are very fine, a
small amount of alum added to the suspension makes filtration faster.
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Fig:1.2 - Separation by filtration
Evaporation
Aim
To separate a non-volatile soluble salt from a liquid or recover the soluble solid solute from the
solution. The solvent is lost into the surroundings.
Experiment
Aim
To separate a non-volatile soluble salt from a liquid or recover the soluble solid solute from the
solution. The solvent is lost into the surroundings.
Principle
Liquids evaporate at all temperatures. Evaporation becomes faster at higher temperatures.
Process
The solution containing the mixture is taken in a china dish and heated gently. Gradually the solvent
evaporates and the solution containing the dissolved solute becomes thicker. The semi-solid mass
left on the china dish is slowly heated to dryness.
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Fig: 1.3 - Evaporation of a solution
Crystallization
This method is used to separate a solid compound in pure and geometrical form. A nearly saturated
solution of an impure substance is prepared in a hot solvent. The prepared solution is quickly filtered
and the filtrate is then allowed to cool slowly in a china dish. The resulting pure crystals that form are
removed with the help of a spatula. They are dried by pressing them between the folds of filter papers
and finally put into a dessicator.
Sublimation
This method is used to separate volatile solids, from a non-volatile solid. The mixture is taken in a
china dish covered with a perforated filter paper on which an inverted glass funnel is placed to collect
the vapours. Upon heating, the substance vapourizes and gets deposited on the walls of the funnel.
The non-volatile substances are left in the dish.
Distillation
Distillation is used for separating the constituents of a liquid mixture, which differ in their boiling
points. Depending upon the difference in the boiling points of the constituents, different types of
distillation like fractional distillation, steam distillation etc. are employed.
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Magnetic Separation Method
Aim
To separate a magnetic component from a mixture containing non- magnetic components.
Experiment
Aim
To separate a magnetic component from a mixture containing non-magnetic components.
Principle
The magnetic component of the mixture is separated with the help of the magnetic attraction.
Process
A magnet is moved over the mixture containing the magnetic substance e.g., iron filings. These get
attracted to the magnet. The process is repeated until the magnetic material is completely separated
from the mixture.
Fig: 1.4 - Separation of a magnetic substance by a magnet
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Gravity method
Aim
To separate mixtures in which components have different densities.
Principle
Particles with higher density settle to the bottom while the lighter particles are separated through
various processes such as winnowing (grain separation) and washing (panning of gold in the river
bed).
Process
Riverbed sand containing fine particles of gold is repeatedly washed in a pan with flowing water. Gold
particles settle to the bottom of the pan because of higher density while lighter sand particles are
washed over the edge of the pan.
Solvent Extraction Method
Organic compounds, which are easily soluble in organic solvents but insoluble or immiscible with
water forming two separate layers can be easily separated. The aqueous solution of the mixture is
mixed with a small quantity of organic solvent in a separating funnel. The separating funnel is
stoppered and shaken strongly. It is allowed to stand for some time. The organic liquid and water
form separate layers, which are collected by opening the stop-cock. The aqueous layer is again
transferred to the separating funnel. The process is repeated with more organic solvent.
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