The effect of temperature on solubility can be explained on the basis cf Le Chatelier's Principle Le Chatelier's Principle states that if a stress (for example, heat, pressure, concentration of one reactant) is applied to an equilibrium, the system will adjust, if possible, to minimize the effect of the stress. This principle is of value in predicting how much a system will respond to a change in external conditions. Consider the case where the solubility process is endothermic (heat added).

solid + heat solution

An increase in temperature puts a stress on the equilibrium condition and causes it to shift to the right. The stress is relieved because the dissolving process consumes some of the heat Therefore, the solubility (concentration) increases with an increase in temperature. If tlr process is exothermic (heat given off).

solid solution + heat

A temperature rise will decrease the solubility by shifting the equilibrium to the left.

How much solute is dissolved in a solution is very important when the solution is being made for a specific use. To say there is a little, a lot, or a bit would not be very accurate if a specific concentration is required. There are a few common and accurate methods used to express concentration. These are density, molarity, normality, and parts per million.

Density

Density is the measure of the mass per unit volume of a material (density = mass/volume) Density is a characteristic of a substance; mass and volume are mt. Mass and volume vary with size but density will remain constant. Temperature will affect the density of a substance and the temperature at which density for that substance was determined is usually reported along with the density value.