Solutions
3.0 Solubility
3.0 Solubility
Solubility of a substance is the maximum amount of solute that can be dissolved in a specific amount of solvent.
It depends on nature of solute, solvent, tempreture and preesure.
Generally, solubility is measured in terms of mole fraction. But, other concentration terms can also be used.
Saturated Solution
It is the solution in which no more solute can be disolved.
If more solute is added to saturated solution, it settles down.
Solubility of solid in liquid
Solute is solid and solvent is liquid.
Dissolution
When solute is added to a solvent, some solute dissolves and its concentration increases in solution. This process is called dissolution.
Crystallisation
Some solute particles collide with solid solute and get separated out, this process is called crystallisation.
When these two process occur at same rate then no more solute can be dissolved at the same temperature and pressure. So, at this stage the solution becomes saturated solution. $$Solute + Solvent \rightleftharpoons Solution$$
Effect of temperature $$Solute + Solvent \rightleftharpoons Solution$$
This equation follows Le Chatelier's principle in nearly saturated solution.
So, for endothermic process solubility will increase with increase in temperature and for exothermic process solubility will increase with decrease in temperature.
As, $\Delta {H_{Solution}}$ = Enthalpy of solution,
| Process | $\Delta {H_{Sol}}$ | Temperature | Solubility |
| Endothermic | Positive | increases | increases |
| Exothermic | Negative | decreases | increases |
Pressure do not effect solid in liquid solution
Like disolves Like
According to this, polar solute are more soluble in polar solvent and non-polar solute are more soluble in non-polar solvent.
Example: $NaCl$ is more soluble in water than in any organic non-polar solvent like ether.
