WATER
Saturated, Unsaturated and Supersaturated
Solution
On the basis of
solubility solutions are classified into three types:
A solution that cannot dissolve anymore of the
solute at a given temperature is called a saturated
solution.
A solution in which
more solute can be dissolved is called an unsaturated
solution.
A solution in which
more solute is present at a given temperature than in a saturated solution is
called a supersaturated solution.
E.g. The maximum
amount of NaCl which can be dissolved in100g of water at 25
is 36g. So if a solution contains 36g of NaCl
dissolved in 100g water then it is a saturated solution. If 10g NaCl is
dissolved in 100g of water at 25,
it is an unsaturated solution. Now if we have a NaCl solution in which 50g of
NaCl is dissolved in 100g of water at 25 then it is supersaturated solution.
Solution: A solution is a homogeneous
mixture of two or more components. The two components of the solution are
called solvent and solute.
Solute: The component which dissolves is known as the solute.
Solvent: The component in which the solute dissolves is known as the solvent.
If the components of
a solution are in the same physical state, then the component which is in
excess is termed as the solvent. If the components exist in different physical
states, then the component which has the same physical state in the pure form
as the solution is called the solvent. For example, when sugar is dissolved in
water to form a sugar solution, sugar is called the solute and water is called
the solvent.
Solute + Solvent = Solution
Aqueous and Non Aqueous Solution
On the basis of the
nature of solvent, solutions are classified into two types: aqueous and non-
aqueous solution.
The solution in
which water is a solvent is called an aqueous
solution.
E.g. NaCl dissolved
in water.
The solution in
which the solvent is any other liquid other than water is called a non -aqueous solvent.
E.g. Iodine
dissolved in ethyl alcohol.
Concentrated and Dilute Solutions
Depending on the
amount of solute solutions are classified into two types: dilute and
concentrated.
The solution in
which the amount of solute present is relatively less compared to the mass of
the solvent is called dilute
solution.
The solution in
which the amount of solute present is relatively more for a given mass of the
solvent is called concentrated
solution.
Solubility
The maximum amount of
solute in grams that can be dissolved in 100g of a particular solvent at a
particular temperature to form a saturated solution is called the solubility of
the solute in that solvent at that temperature.
E.g. 65.0g of KNO3
on dissolving in 100g of water at 40 produce a saturated solution. Thus the
solubility of KNO3 in water at 40 is 65.0g. Mathematically,
Solubility of a solute at t = 
Illustration 1: When 20g of a saturated solution of KCl
at 20,
is evaporated to dryness, a solid residue of 5g is left behind. Find the
solubility of KCl.
Solution: Given: Mass of solution = 20g
Mass of solute
= 5g
Mass of water
in the solution = 20g – 5g = 15g
Solubility = 
= 
= 33.3g
Factors Affecting Solubility
i. Nature
of Solute: Different substances dissolve to
different extents in the same volume of a given solvent.
E.g. The solubility of NaCl and KNO3
in 100g of water at 40
is 36.0g and 65.0g respectively.
ii. Nature
of Solvent: The solubility of a solute depends on
the nature of solvent. Polar compound dissolves in a polar solvent while a non-
polar compound dissolves in a non- polar solvent. Thus we can say ‘like
dissolves like”.
E.g. NaCl dissolves in water but is
insoluble in carbon disulphide whereas sulphur dissolves in carbon disulphide
but is insoluble in water.
iii. Temperature:
The solubility of most of the solutes increases with temperature but the
solubility of few substances may decrease or remain same with increase in
temperature. It is usually seen that the solubility of those solutes whose
dissolution process is exothermic, decreases with increase in temperature while
those solutes whose dissolution process is endothermic, increases with increase
in temperature.
iv. Size
of Solute Particles: The smaller the size of solute
particles, greater the solubility of the solute.
v. Stirring:
Stirring increases the rate of dissolution of the solute.
Solubility
Curve
A solubility curve is a line graph that
plots the change in the solubility of a solute in a particular solvent against
temperature.
Solubility of Gases
The solubility of a gas in a liquid
depends on pressure and temperature.
Pressure:
At any given temperature, the mass of a gas dissolved by a fixed volume of liquid
is directly proportional to the pressure on the surface of the liquid. This is
known as the Henry’s law.
Temperature: An increase in temperature of water
decreases the solubility of a gas.
Water of Crystallisation
The water molecules which get
loosely attached to a salt during crystallisation of the salt from their
aqueous solution are called water of crystallisation.
Efflorescence
The property by virtue of which some
substances loose water of crystallisation partially or wholly when exposed to
air is called efflorescence.
Efflorescent Substances
Those substances which lose their
water of crystallisation partially or wholly when exposed to air are called efflorescent
substances. Thus, they lose their crystalline shape and become powdery.
E.g. Washing soda (Na2CO3.10H2O),
Glauber’s salt (Na2SO4.10H2O), Epsom salt (MgSO4.
7H2O)
Hygroscopic Substance
Substances which can absorb
moisture from the atmosphere are called hygroscopic substance.
E.g. conc. H2SO4,
Phosphorus pentoxide (P2O5), Quicklime (CaO), Silica gel
Deliquescence
The property by virtue of which
some substances when exposed to air absorb moisture from the air and dissolve
in it is called deliquescence. Deliquescence occurs when the vapour pressure of
the salt is much lower compared to atmospheric vapour pressure.
Deliquescent Substances
Those substances which when
exposed to air absorb moisture from the air to become moist, and ultimately dissolve
in it are called deliquescent substances.
E.g. conc. H2SO4,
Caustic soda (NaOH), caustic potash (KOH), Magnesium chloride (MgCl2),
Zinc chloride (ZnCl2), Ferric chloride (FeCl3), etc.
Drying agent: Those substances which remove moisture from other
substances are called drying agents or desiccating agents.
E.g. conc. H2SO4,
Phosphorus pentoxide (P2O5), Quicklime (CaO), Silica gel,
etc.
Dehydrating agent: Those substances which remove water molecules
from compounds are called dehydrating agents.
E.g. Conc. H2SO4,
Water is
regarded as a universal solvent.
• Depending
upon the behavior of water towards soap, water may be classified as soft or
hard water.
• Degree of hardness is expressed in
ppm.
Types
of hardness of water
1. Temporary
hardness – due to bicarbonates of Ca and Mg.
2. Permanent
hardness – due to chlorides and sulphates of Ca and Mg.
Methods
of removing hardness
Temporary
hardness
1. By boiling
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