Solutions
Solutions : It is the homogeneous mixture of two or more than two components.
Exam :
Mixture of sugar and water.
Solvent : The component of a solution present
in the huge quantity is referred to as solvent which determines the
physical state of the solution.
Solute : The components of a solution present in the lesser amount
and get easily dissolved in solvent is
referred as solute.
Exam : In the case of lemonade Water is the solvent whereas
salt/sugar are the solute.
Types of solutions
Solutions can be
broadly categorized into two types :-
Homogeneous solutions : Solutions whose
components have uniform composition and properties throughout the solution are
known as homogeneous solution.
E.g : solution of
salt or sugar in water, cough syrup, are homogeneous mixture of chemicals and
dyes, etc.
Homogenous solution of
sugar dissolved in water.
Heterogeneous solutions : Solutions whose
component have non-uniform composition
and properties throughout the solution are known as heterogeneous solution.
E.g : solution of water and sand, solution of oil
and water, water and chalk powder, etc.
Type of solution
|
Solute
|
Solvent
|
Example
|
Gaseous
|
Gas
|
Gas
|
Hydrogen and nitrogen mixture
|
Liquid
|
Gas
|
Chloroform with nitrogen gas
|
|
Solid
|
Gas
|
Camphor in nitrogen gas
|
|
Liquid
|
Gas
|
Liquid
|
Oxygen in water
|
Liquid
|
Liquid
|
Ethanol in water
|
|
Solid
|
Liquid
|
Glucose in water
|
|
Solid
|
Gas
|
Solid
|
Hydrogen solution in palladium
|
Liquid
|
Solid
|
Amalgam of mercury with sodium
|
|
Solid
|
Solid
|
Dissolved copper in gold
|
Percentage compositions
Mass percentage
Mass percentage can be defined as the percentage of mass of
the component of the solution present in total mass of the solution.
Volume percentage
Volume percentage can be defined as percentage of volume of the
component of the solution present in total mass of the solution.
Mass by volume percentage
Mass by volume percentage can be
defined as the mass of solute dissolved in 100 mL of the solution.
For instance, mass by
volume percent of a solution with 1 g of solute dissolved in 100 mL of solution will
be 1% or 1% (mass/volume).
Parts per million
Parts per million can be defined as the ratio of number of
parts of the component to the total number of parts of all components of the
solution multiplied by 106. It is denoted
by ppm.
v It is used to express concentration of a solution where
solute is present in trace.
v For instance, concentration of pollutants in water or
atmosphere is expressed in terms of
g mL-1 or ppm.
Mole fraction
Mole fraction can be defined as the ratio of number of moles
of the component in the solution to the total number of moles of all components
in the solution.
Molality
Molality (m) can be defined as the number of moles of
solute dissolved in per Kg of solvent.
Unit – molal or m.
Molarity
Molarity (M) can be defined as the number of moles of solute dissolved in per
liter of solution.
It is function of temperature due to the dependence of
volume on temperature whereas Mass %, ppm,
mole fraction and molality are
independent of temperature because mass does not depend on temperature.
Unit – molar or M.
Solubility
Solubility is a
physical property of a solution. It can be defined as the maximum amount of
solute that can be dissolved in a specific amount of solvent at constant
temperature and pressure.
This property of solution
depends upon the factors like:
v The nature of solute and solvent and the interaction between them : The stronger the attractions between solute and solvent
molecules, the greater will be the solubility.
v Molecular size of solute : Larger molecules are more difficult to dissolve in solvents
whereas the smaller molecules dissolve easily and are more soluble in solvents.
v
Polarity : Polar solvents (having bonds with different electro
negativities) like Water, ethanol, formaldehyde dissolve polar solutes, whereas
non-polar solvents (having bonds with similar electro negativities) like
pyridine, toluene, and hexane dissolve non-polar solutes.
v Temperature : Rise in temperature increases the solubility.
v
Pressure : Rise in pressure increases the solubility.
Solubility of a solid in a
liquid
Solution of sugar
or salt dissolved is a common example of solubility of a solid in liquid. But
it is not necessary that all solids will dissolve in liquid.
For instance, solids like naphthalene and
anthracene do not dissolve in water but dissolves easily in benzene but sugar
and salt does not dissolves in benzene. This is because it is property of
solution that polar solutes dissolve in polar solvents like Water, ethanol,
formaldehyde and chloroform whereas non polar solutes dissolves in non-polar
solvents like pyridine, toluene, and hexane. This phenomenon can be easily defined
as like dissolves like.
v
The phenomenon of
increase in the concentration of solution due to dissolving of solid solute to
the solvent is known as dissolution.
v
The phenomenon of
collision of solute particles in a solution resulting in the separation of the
solute particles from the solution is known as crystallization.
v
According to Le
Chateliers Principle in a saturated solution, if the
dissolution process is endothermic (Δsol H >
0), the solubility should increase with rise in temperature but if the dissolution
process is exothermic (Δsol H > 0)
the solubility should decrease.
v
Pressure does not have
crucial effect on solubility of solids in liquids because they remain
unaffected to pressure due to the high incompressibility of solids and liquids.
Solubility of a gas in a liquid
The amount of gas that can be
dissolved in a particular amount of liquid at constant temperature and pressure
is called solubility of gas in liquid.
Solubility of gas in liquid is
highly affected by temperature and pressure.
v
Increase in
temperature reduces the solubility of gases in liquids because on dissolving
gas molecules in liquid the process of dissolution is similar to condensation
leading to the evolution of heat. Therefore, dissolution is an exothermic
process, due to which the solubility decreases with increase of temperature.
v
Increase in pressure
by compressing the gas to a smaller volume increase the number of
gaseous particles per unit volume over the solution and also the rate at which the gaseous particles are striking the surface of solution to enter it leading to the increase in the solubility of gases.
gaseous particles per unit volume over the solution and also the rate at which the gaseous particles are striking the surface of solution to enter it leading to the increase in the solubility of gases.
Solubility of gas in liquid can be explained by Henry’s law : -
Henry’s law
According to this
law, “At constant temperature and pressure, the solubility of gas in liquid
will be directly proportional to the pressure applied over it.
It can also be stated as - the partial pressure of the gas
in vapour phase (p) is proportional to the mole fraction of the gas (x)
in the solution.
Mathematically,
p = KH χ
where, KH = Henry’s
law constant.
v
At same temperature
different gasses have different KH
v
Value of KH increases with the increase in temperature
therefore solubility of gases increases with decreasing temperature. Due to
this reason cold water is more sustainable for aquatic life than warm water.
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