Question

What are the solubility curves? Give their uses.

Answer 1

The solubility curve tells the effect of temperature on the solubility in water of different compounds or elements. There are three categories of various substances for the solubility in water.

Complete step by step answer:
The solubility curve tells the effect of temperature on the solubility.
Based on the effect of temperature on solubility in water, the ionic substances are divided into three categories:
(a)- Substances whose solubility increases on increasing the temperature: Most of the substances like $NaN{{O}_{3}}, KN{{O}_{3}}, NaCl, KCl$, etc fall into this category. The reason is this behavior is that in all these cases, the process of dilution is endothermic i.e.
$Solute+Solvent+Heat\rightleftharpoons Solution$

(b)- Substances whose solubility decreases when temperature increases: There are some substances that come in this category. These are cerium sulfate, lithium carbonate, sodium carbonate monohydrate ($N{{a}_{2}}C{{O}_{3}}.{{H}_{2}}O$), etc. whose solubility decreases on increasing the temperature. This is due to the fact that this process is exothermic.

(c)- Substances whose solubility does not increase or decreases continuously: There are some substances which on heating change at a particular temperature from one polymorphic form to another or from one hydrated form to another ($CaC{{l}_{2}}.6{{H}_{2}}O\to CaC{{l}_{2}}.4{{H}_{2}}O\to CaC{{l}_{2}}.2{{H}_{2}}O$) or from hydrated form to anhydrous form ($N{{a}_{2}}S{{O}_{4}}.10{{H}_{2}}O\to N{{a}_{2}}S{{O}_{4}}$).
When the solubilities are plotted against temperature, the curve obtained is the solubility curve.
It can be used to calculate the mass of the crystals deposited and the solubility of the solute at any temperature.

Note: Pressure has very little effect on the solubility of a solid in a liquid because solids and liquids are highly incompressible. There are two forms of the solubility curve: Continuous and Discontinuous.