Solution and Its Component
A solution may be defined as a homogeneous mixture of two or more non-reacting substances whose composition can be varied within certain limits.
For example, air is a homogeneous mixture of a number of gases. Its two main constituents are oxygen (21%) and nitrogen (78%).
It may be noted that all mixtures are not solutions. If a mixture is to be called a solution, it must satisfy the following two conditions:
- Components should be non-reacting.
- Should be homogeneous.
1.0Components of A Solution
The substances present in a homogeneous solution are called components of the solution. A solution basically has two components i.e. a solvent and a solute and such a solution is called binary solution.
(a) Solute:
The component of the solution which dissolves in the solvent, is called solute. Usually, solute is the smaller component of the solution, for example, solution of iodine in alcohol, known as 'tincture of iodine', iodine is the solute in this solution.
Similarly, in carbonated drinks (soda water), carbon dioxide gas is the solute.
(b) Solvent
The component of a solution which dissolves the other component in itself, is called solvent. Usually, a solvent is the larger component of the solution. For example, a solution of sugar in water is a solid in liquid solution. In this solution, sugar is the solute and water is the solvent.
The common examples of aqueous solutions are
(i) common salt dissolved in water.
(ii) sugar dissolved in water.
(iii) acetic acid dissolved in water (called vinegar).
The common non-aqueous solvents are alcohol, carbon disulphide, carbon tetrachloride, acetone, benzene, etc. Examples of non-aqueous solutions are
(i) Iodine dissolved in carbon tetrachloride.
(ii) Sulphur dissolved in carbon disulphide.
(iii) Bromine dissolved in chloroform.
(iv) Sugar dissolved in alcohol, etc.
2.0Characteristics of A Solution
(1) A solution is a homogeneous mixture.
(2) The size of solute particles in a solution is extremely small. It is less than 1 nm (10–9 m) in diameter.
(3) The particles of a solution cannot be seen even with a microscope.
(4) The particles of a solution pass through the filter paper. So, a solution cannot be separated by filtration.
(5) The solutions are very stable. The particles of solute present in a solution do not separate out on keeping it undisturbed.
(6) A true solution does not scatter light passing through the solution (because its particles are very small).
(7) The components of a solution do not chemically react with one another.
(8) A solution is always transparent in nature.
(9) From a true solution, the solute can be easily recovered by evaporation or crystallisation.
3.0Methods to Express Concentration of Solution
The concentration of a solution is the amount of solute present in a given quantity of the solution or solvent.
In a solution the relative proportion of the solute and solvent can be varied. Depending upon the amount of solute present in a solution, it can be called a dilute, concentrated or a saturated solution.
There are many ways to express the concentration of a solution. But the most common method for expressing the concentration of a solution is called the percentage method.
(i) Mass by mass percentage(w/w)
The mass of the solute in grams dissolved in 100 g of the solution.
Mass by mass percentage of a solution =
Mass of solution = Mass of solute + Mass of solvent
(ii) Mass by volume percentage(w/v)
The mass of the solute in grams dissolved in 100 mL of the solution.
Mass by volume percentage =
(iii) Volume by volume percentage or simply volume percentage(v/v).
The volume of the solute in millilitres dissolved in 100 mL of the solution.
Volume by volume percentage =
4.0Classification of Solutions on The Basis of Amount of Solute
It is not possible to dissolve just any amount of a solute in a given amount of solvent. For example, when we add sugar to water, the crystals of sugar keep on going into the solution in the beginning. But after some time, no mass of sugar dissolves provided the temperature is kept constant.
Saturated Solution
A solution which at a given temperature dissolves as much solute as it is capable of dissolving is said to be a saturated solution.
For example, At 30°C, 55 g of common salt dissolves in 100 g of water. However, if more of the common salt is added to the above solution, it does not dissolve. In such a situation, the solution of common salt containing 55 g of salt in 100 g of water is a saturated solution at 30°C.
- If a saturated solution at some particular temperature is heated, the solution becomes unsaturated, because of the increase in solubility.
- If a saturated solution at some higher temperature is cooled, it remains saturated. The excess solute comes out of the solution and deposits itself in the form of crystals.
Unsaturated Solution
When the amount of solute contained in a solution is less than the saturation level, the solution is said to be an unsaturated solution.
For example, at 30°C, if 45 g of common salt is dissolved in 100 g of water, such a solution is capable of dissolving more of the common salt, then such a solution is called an unsaturated solution.
Supersaturated Solution
A solution which contains more of the solute than required to make a saturated solution, is called a supersaturated solution.
5.0Suspension
A suspension is a heterogeneous mixture in which the solid particles are spread throughout the liquid without dissolving in it. The particles have a tendency to settle down at the bottom of the container and can be filtered out. For example,
(1) Chalk-water mixture is a suspension of fine chalk particles in water.
(2) Muddy water is a suspension of soil particles in water.
Properties of Suspension
(1) A suspension is a heterogeneous mixture.
(2) The size of solute particles in a suspension is quite large. It is larger than 1000 nm or 10–6 m in diameter.
(3) The particles of a suspension can be seen easily with naked eyes and under a microscope.
(4) A suspension scatters a beam of light passing through it (because its particles are quite large thus makes its path visible).
(5) The particles of suspension settle down when the suspension is kept undisturbed.
(6) The process of settling down of suspended particles under the action of gravity is called sedimentation. So, suspensions are unstable. After sedimentation, it does not scatter light any more.
(7) The solid particles present in the suspension can be easily separated by ordinary filter papers. No special filter paper is needed for the purpose.
(8) Suspensions are either opaque or translucent.
6.0Solubility
The maximum amount of solute in grams which can be dissolved in 100 g of the solvent at a given temperature to form a saturated solution is called solubility of the solute in that solvent at that particular temperature.
Solubility of some substances at 20°C
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