Solutions
Solubility
The maximum amount of solute which can be dissolved in a specified amount of solvent at a given temperature is called the solubility of a substance (solute).
Solubility depends on the following factors:
- Nature of solvent
- Nature of solute
- Temperature Pressure
Solubility of a Solid in a Liquid
Like Dissolves Like
Every solid does not dissolve in every liquid. Only polar solute (solid) dissolves in polar liquid (solvent) and non-polar solute (solid) dissolved in non-polar liquid(solvent).
If intermolecular attractions of solute and solvent are similar, then that solute (solid) dissolve in that very solvent.
Example – Sugar and common salt readily dissolve in water while naphthalene and anthracene do not. Naphthalene and anthracene dissolve in benzene while common salt and sugar do not.
Conditions for a solute to dissolve in a solvent:
(1)Solute and solvent both should be polar or non polar.
(2)The intermolecular attractions of both the solute and solvent should be similar.
Dissolution
Dissolution means to dissolve. When a solid is added to a solvent (liquid); the concentration of solution increases because of dissolving of some of the solute. This process is called dissolution.
Crystallization:
In the process of dissolution some of the particles of solute collide with the solid particles of solute and separated out of the solution, is called the crystallization.
Dynamic equilibrium:
In the process of dissolution and crystallization the stage in which the rate of both of the process started and keeps on occurring at same rate, is called the dynamic equilibrium.
In the condition of dynamic equilibrium number of solid particles mixing in the solution becomes equal to the solute particles separating out from the solution. The state of dynamic equilibrium can be shown by using following equation:
Solute + Solvent ⇆ Solution
Similar process occurs when a gas is dissolve in liquid.
Saturated Solution
At the stage of dynamic equilibrium the concentration of solute remains constant in solution under given temperature and pressure, is called saturated solution.
The solution in which no more solute can be dissolved under the given conditions, i.e. temperature and pressure is called saturated solution.
Unsaturated solution:
The solution in which more solute can be dissolved under the given conditions, i.e. temperature and pressure, is called unsaturated solution.
Effect of temperature on the solubility of solid in a liquid:
Solubility of a solid into liquid increases with increase in temperature; and vice versa.
Explanation:
The process of dissolution is either endothermic or exothermic.
In the endothermic process of dissolution (dissolving of solute in solvent), solubility increases with rise in temperature.
In the exothermic process of dissolution, solubility decreases with rise in temperature.
Dynamic equilibrium of the solute, solvent and solution must follow Le Chatelier’s Principle.
Le Chatelier’s Principle states that if the dynamic equilibrium is disturbed by changing of conditions, the position of equilibrium moves to counteract the change.
This means if any of the condition of dynamic equilibrium, i.e. temperature, pressure or concentration or volume, the equilibrium shifts accordingly to adjust or counteract the change.
Le Chatelier’s Principle is also known as simply Chatelier’s Principle or ‘The Equilibrium Law’.
Effect of pressure on the solubility of solid into liquid:
Pressure has no effect the solubility of solid into liquid.
Explantion:
As solids and liquids are highly incompressible, hence there is no effect of pressure in solubility of solid into liquid.
In other words, pressure has no effect on solubility of solid into liquid, because solid and liquid cannot be compressed easily.
Reference: