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Is matter around us pure?
Pure substance
Chemically pure substance is a kind of matter that cannot be separated into other
kinds of matter by any physical process
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Meaning of pure substance different for a common man than to a chemist
For a common man, pure substance means that it is not adulterated
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But for a chemist, any milk is not a pure substance
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Purity of a given substance
A pure substance always has the same colour, taste or texture at a given temperature
and pressure
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For example, pure water boils at 373K at 1 atmospheric pressure
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Mixture
If two or more substances (elements, compounds or both) mixed together in any
proportion, do not undergo any chemical change, but retain their characteristics, the
resulting mass is called mixture
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Examples: A mixture of sand, salt and sulphur is a heterogeneous mixture
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Homogeneous mixture
A mixture in which different constituents are mixed uniformly is called homogeneous
mixture
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Similarly, all solutions are homogeneous mixtures
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Variable composition: The constituents of a mixture are present in any ratio
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2
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The constituents of
a mixture do not bind each other by chemical bonds
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e
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3
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Example: The properties of air are midway between properties of nitrogen and
oxygen
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Homogeneity: Most of the mixtures are heterogeneous, i
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, their constituents
are not
spread evenly throughout
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Example: In the mixture of iron and sulphur, at some places iron is more and at
some places sulphur is more
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Separation: Generally, the constituents of mixture can be separated by
employing
suitable physical means
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6
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Example: On mixing iron and sulphur, heat energy is neither absorbed
nor evolved
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A
true solution is a homogeneous mixture of two or more substances
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e
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, sugar dissolved in water, iodine in ethyl alcohol (tincture)
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e
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This path of light is not visible in a solution
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A true solution can completely pass through filter paper as particle size of
solute is far smaller than the size of pores of filter paper
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A true solution is homogeneous in nature
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Thus, the true solution is stable in nature
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Solute
The substance(s) present in smaller proportion in a solution is called solute
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If a
homogeneous mixture or a solution is formed by dissolving 2 g salt in 100 g water,
then salt is the solute and wateris the solvent
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Differentiate between a saturated solution and an unsaturated solution
Saturated solution
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Unsaturated solution
A solution in which more of the solid can be dissolved at the given temperature is
called an unsaturated- solution
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If to a given solution, more salt is added and it dissolves, then it is unsaturated
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For example,
brass is a mixture of approximately 30% zinc and 70% copper
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Concentration of solution = Amount of solute / Amount of solution Or Amount of
solute/Amount of solvent
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It is normally expressed as mass percent or as
volume percent
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Volume Percent
Volume percent of a solution may be defined as: the number of parts by volume of
one component (solute or solvent) per 100 parts by volume of the solution
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Calculate the concentration
in terms of mass by mass percentage of the solution
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Mass of solute (salt) = 40g, Mass of solvent (water) = 320g
We know, Mass of solution = Mass of solute + Mass of solvent = 40 g +320 g = 360 g
Mass percentage of solution

 

Q
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What is
mass percent of urea in the solution?
Ans = 5%
Q
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Ans = mass of cane sugar = 62
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5g
Q
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Calculate the
concentrate of the solution
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45%
Q
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Calculate its
concentration of the solution in terms of volume percent
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25%
Suspensions
A heterogeneous mixture of insoluble particles of solute, spread throughout a solvent,
is called suspension
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The particles have
a tendency to settle down at the base of solvent and can be filtered out, because
their size is bigger than the size of the pores of filter paper
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Slaked lime suspension used for white washing has particles of slaked lime
suspended in water
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Characteristics of Suspensions:
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The size of particles is more than 10-5 cm in diameter and hence can be seen
with unaided eye
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The particles of suspension settle down, when the suspension is kept
undisturbed
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Thus,
we
can
say that suspensions are unstable
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An excessive amount of scattering takes place in suspensions, because of bigger
size of particles
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Colloidal Solutions or Colloids:
A neither heterogeneous solution in which the particle size is in between 10-7 cm to
10-5 cm, such that the solute particles neither dissolve nor settle down in a solvent is
called colloidal solution
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Characteristics of Colloidal Solutions:
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The size of a colloidal particle is in between 10-7 cm and 10-5 cm
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The particles of a colloidal solution do not settle down with the passage of
time
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The particles of a colloidal solution cannot be recovered by crystallization or
evaporation
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The particles of a colloidal solution can easily pass through filter paper and
hence cannot be separated by filtration
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e
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Colloidal solutions are not transparent, but translucent in nature
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Tyndall effect:
When strong beam of light is passed through a true solution taken in a beaker placed
in a dark room, the path of light through the solution is dark
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This is called Tyndall effect
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