SOLUTIONS AND THEIR TYPES

Homogeneous mixture: A mixture in which composition and properties are uniform throughout is called a homogeneous mixture.

Solution : A homogeneous physical mixture of two or more substances is called a solution. A solvent and one or more solutes make up every solution.

Solvent: The element that makes up the majority of a solution is referred to as a solvent. Every solution consists of a solvent and one or more solutes... The physical state of a solution is determined by the solvent.

Solute: All the components other than solvent present in a solution are called the solute.

Binary solution: Solutions consisting of only two components are called binary solutions.

Types of solutions

I. Solid solutions: Solutions in which the solvent is solid are called solid solutions.

There are three types.

(a) Solution of solid in solid: Solid solute dissolved in a solid solvent is called a solution of solid in solid. e.g. (i) Brass (Cu dissolved in zinc). (ii) Copper dissolved in gold.

(b) Solution of liquid in solid: A liquid solute dissolved in a solid solvent is called a solution of liquid in a solid. e.g. Sodium amalgam.

(c) Solution of gas in solid: The solution of the gas solute in a solid solvent is called a solution of the gas in solid. e.g.

Hydrogen is absorbed in metals like Pt. Pd. Ni, etc.

II. Liquid solutions: Solutions in which liquid is used as a solvent are called liquid solutions. There are three types,

(a) Solution of solid in liquid: The solution of the solid solute in a liquid solvent is called a solution of solid in a liquid.

e.g. (i) Solution of salt in water. (ii) Solution of sugar in water.

(b) Solution of liquid in liquid: The solution of the liquid solute in a liquid solvent is called a solution of liquid in liquid.

e.g. Solution of ethanol in water.

(c) Solution of gas in liquid: The solution of

the gas solute in a liquid solvent is called a solution of the gas in a liquid.

e.g. (i) Solution of CO2 in water (soda water). (ii) Solution of oxygen dissolved in water.

III. Gaseous solutions: Solutions in gaseous solvents are called gaseous solutions. There are three types,

(a) Solution of solid in gas: A solution in which a solid solute is dissolved in a gaseous solvent is called a solution of solid in gas. e.g. (i) Dust particles in the air. (ii) Camphor vapour in nitrogen gas.

(b) Solution of liquid in gas: A solution in which liquid solute is dissolved in a gaseous solvent is called a solution of liquid in gas.

e.g. (i) Moisture (water vapour) in air.

(ii) Chloroform in nitrogen gas.

(c) Solution of gas in gas: A solution in which a gaseous solute is dissolved in a gaseous solvent is called a solution of the gas in gas. e.g. Air (mixture of nitrogen, oxygen, and other gases).

Solubility

The maximum amount of solute that can be dissolved in a the specific amount of solvent at a particular temperature is called the solubility of that substance, or, the concentration of the solubility of a solute in a saturated solution.

Generally, Solubility is denoted by 'S' moles per liter.

Factors Affecting Solubility

Solubility depends on the following factors

(i) Nature of solute

(ii) Nature of solvent

(iii) Temperature

iv) Pressure

(i) Nature of solute: For a given solvent solubility of different solutes is different.

For example chloride (table salt) and sucrose (sugar) dissolve readily but benzene and toluene are insoluble in water.

Generally, a solute dissolves in a solvent when intermolecular interactions in both are the same. This is called like dissolves in like. e.g. polar solutes dissolve in polar solvents.

(ii) Nature of solvent: Solubility of the same solvent for different solutes is different. In Benzene, naphthalene and anthracene dissolve readily but sodium chloride and sugar do not dissolve in benzene.

(iii)Temperature: The solubility of a particular solute in a particular solvent is largely affected by temperature.

According to the Le-Chateliers principle solubility of a solid in liquid increases with the rise in temperature if the dissolution process is endothermic.

And solubility decreases with a rise in temperature if the dissolution process is exothermic.

However, most dissolution processes of solids" in liquid are endothermic and hence solubility increases with the temperature rise.

Solubility of gases: The solubility of gases in liquid decreases with an increase in temperature.

Cause: Dissolution of gas is similar to the condensation of gas to a liquid state and always an exothermic process. Hence according to the Le-Chateliers principle, solubility should decrease with the increase in temperature.

This is why aquatic species are more comfortable in cold water (in the winter season) than in warm water (summer season).

(iv) Pressure :

(a) The solubility of solids in liquids is not significantly impacted by pressure. Reason: Changes in pressure do not affect extremely incompressible solids and liquids.

(b) Solubility of gases in liquids is greatly affected by pressure: Solubility of gases increases with the increase of pressure.

Cause: When pressure over the gas is increased, the volume of gas decreases. The number of gaseous particles per unit volume increases and hence the rate at which gaseous particles enter the solution increases and the number of gaseous particles coming out of the solution decreases. This is why the solubility of gases in liquid cases with increasing pressure.