Question

(a) Define solubility of a substance. How does it vary with temperature ?
(b) What do you understand by the statement " the solubility of copper sulphate in water at 20°C is 20.7 g" ?
(c) What is the effect of temperature on the solubility of solids in liquids ?

Answer 1

Solubility is a property of a solid, liquid, or gaseous chemical solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution.
Solubility of a given solute in a given solvent depends on temperature. For many solids dissolved in liquid water, the solubility increases with temperature up to 100°C. In liquid water at high temperatures (e.g., that approaching the critical temperature), the solubility of ionic solutes tends to decrease due to change in the property and structure of liquid water. The lower dielectric constant results in a less polar solvent.
Gaseous solutes exhibit more complex behavior with temperature. As the temperature is raised, gases usually become less soluble in water (to minimum, which is below 120°C for most permanent gases), but they are more soluble in organic solvents.

(b) This statement means that 20.7 gm of copper sulphate can be dissolved in 100 gm of water at 20°C.

(c) Solubility of solids in liquids generally increases on increasing the temperature and decreases on decreasing the temperature of the solvent.