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Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ®1. SOLUTIONS
Solutions are homogeneous mixtures containing two or more components. Generally, the component
that is present in larger quantity is called solvent. Solvent determines the physical state of the solution. One
or more components present in the solution other than solvent are called solutes. [Or, the substance which is
dissolved is called solute and the substance in which solute is dissolved is called solvent].
Solutions containing only two components are called binary solutions. Here each component may be
solid, liquid or in gaseous state. Based on this, solutions are of the following types:
Types of Solution Solute Solvent Examples
Gas Gas Mixture of O2 and CO2
Gaseous solutions Liquid Gas Chloroform mixed with nitrogen gas, water-vapour in air
Solid Gas Camphor in nitrogen gas, naphthalene in air
Gas Liquid Oxygen dissolved in water, soda water
Liquid solutions Liquid Liquid Alcohol dissolved in water, dilute acids and alkalies
Solid Liquid Salt in water, glucose in water
Gas Solid Hydrogen in Pd, Pt, Ni etc
Solid solutions Liquid Solid Amalgam of mercury with sodium
Solid Solid Gold ornaments, alloys of metals
Concentration of Solutions
Composition of a solution can be expressed in terms of concentration. Concentration is defined as the
number of moles of solute present per litre of the solution. The concentration of a solution can be expressed
by the following ways:
(i) Mass percentage (w/w): It is defined as the mass of the component present in 100g of the solution.
i.e. Mass % of a component = Mass of the component in the solution × 100
Total mass of the solution
For e.g. 10% aqueous solution of glucose by mass means that 10 g of glucose is dissolved in 90 g of water
resulting in a 100 g solution.
Concentration described by mass percentage is commonly used in industrial chemical applications.
(ii) Volume percentage (v/v): It is defined as the volume of a component present in 100 mL of the
solution.
i.e. Volume % of a component = Volume of the component ×100
Total volume of solution
For example, 10% ethanol solution in water means that 10 mL of ethanol is dissolved in 90 mL of water such
that the total volume of the solution is 100 mL.
Concentration of solutions containing liquids is commonly expressed in this unit.
(iii) Mass by volume percentage (w/v): It is the mass of solute dissolved in 100 mL of the solution.
It is commonly used in medicine and pharmacy.
Mass/volume % of a component = Mass of the component in the solution × 100
Total volume of the solution
(iv) Parts per million (ppm): When a solute is present in trace quantities (i.e. very small amounts), its
concentration is expressed in parts per million (ppm). It is defined as the number of parts of a
particular component in million parts of the solution.
i.e. Parts per million (ppm) = Number of parts of the component × 106
Total number of parts of all the components of the solution
Concentration in parts per million can be expressed as mass to mass, volume to volume and mass to volume.
+2 Chemistry Notes - Prepared by ANIL KUMAR K L, APHSS ADICHACHANALLOOR Page 3
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The concentration of pollutants in water or atmosphere is expressed in terms of μg mL –1 or ppm. [μg is
microgram]
(v) Mole fraction (χ): It is defined as the ratio of the number of moles of a particular component to the
total number of moles of the solution.
Mole fraction of a component = Number of moles of the component
Total number of moles of the solution
For example, in a binary solution, if the number of moles of A and B are n A and nB respectively,
then the mole fraction of A (χA) = nA
(nA + nB)
and that of the component B (χB) = nB
(nA + nB)
χA + χB = 1
i.e. in a given solution sum of the mole fractions of all the components is unity. If there are i components,
then
χ1 + χ2 + χ3 + .................. + χi = 1
Mole fraction is useful in describing the calculations involving gas mixtures.
(vi) Molarity (M): It is defined as the number of moles of solute dissolved per litre of solution.
i.e. Molarity (M) = Number of moles of solute (n)
Volume of solution in litre (V)
For example, 1 M (molar) NaOH solution means that 1 mol (40g) of NaOH is dissolved in one litre of solution.
(vii) Molality (m): It is defined as the number of moles of the solute present per kilogram (kg) of the solvent.
i.e. Molality (m) = Number of moles of solute
Mass of solvent in kg
For example, 1 molal (m) solution of KCl means that 1 mol (74.5 g) of KCl is dissolved in 1 kg of water.
Among the different methods for expressing the concentration of solution, mass percentage, ppm (in
terms of mass), mole fraction and molality are independent of temperature; whereas molarity, mass by
volume percentage and volume percentage are depend on temperature. This is because volume depends on
temperature and the mass does not.
SOLUBILITY
Solubility of a substance is its maximum amount that can be dissolved in a specified amount of solvent
at a particular temperature. It depends upon the nature of solute, nature of the solvent, temperature and
pressure.
Solubility of a Solid in a Liquid
It is observed that polar solutes dissolve in polar solvents and non-polar solutes in non-polar solvents.
In general, a solute dissolve in a solvent if the intermolecular interactions are similar in the two or the general
principle related to solubility is that “like dissolves like”.
Saturated and Unsaturated solutions
When a solid solute is added to the solvent, some solute dissolves and its concentration increases in
solution. This process is known as dissolution. Some solute particles in solution collide with the solid solute
particles and get separated out of solution. This process is known as crystallisation. After sometime, the rate
of dissolution and crystallization becomes equal and a dynamic equilibrium is reached. At this stage the
concentration of solute in the solution remain constant and such a solution is called saturated solution.
A solution in which no more solute can be dissolved at the same temperature and pressure is called a
saturated solution. For such a solution, the concentration of the solution is equal to its solubility.
A solution in which more solute can be dissolved at the same temperature is called an unsaturated solution.
Effect of temperature on the solubility of a solid in a liquid
The solubility of a solid in a liquid mainly depends on temperature. Since the dissolution of a solid in a
liquid is an equilibrium process, it should follow Le Chateliers Principle. In general, if in a nearly saturated
+2 Chemistry Notes - Prepared by ANIL KUMAR K L, APHSS ADICHACHANALLOOR Page 4
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