Temperature and Solubility
Most salts show an increase in solubility with increasing temperature. Some change very little and some few show decreased solubility with increasing temperature. Below is a graph of some common examples.
Some interesting situations occur when the the pure solid state is a hydrate. As the temperature increases a point might be reached where the hydrate becomes unstable and begins to lose water. The new form will have a different solubility curve with temperature. The solubility of Na2SO4× 10H2O increases rapidly with increasing temperature, from 5 g of Na2SO4 per 100 g of water at 0° to 55 g at 32.4° C. Above 32.4° C the stable form is Na2SO4. The solubility of the anhydrous form decreases as the temperature increases.
Another example is borax. Just as there are three forms, Na2B4O7× 10H2O, Na2B4O7× 5H2O, and Na2B4O7× 4H2O there are three solubility curves. Other examples are CaCl2× nH2O, Na2CO3× nH2O, and FeSO4× nH2O.