Question

Name a substance whose solubility is decreases with rise in temperature \[?\]

Answer 1

Hint: A chemical substance is a form of matter having constant chemical composition and characteristic properties. Simply a substance is a pure single form of matter. It cannot be separated into other kinds of matter by any physical process. The substance must be composed of atoms and molecules. The substance must have a particular amount of weight, mass and volume.
The rise in temperature of a substance depends on the quality of heat supplied, the mass of the substance and the nature of the substance.

Complete answer:
The solubility of solute in a solution increases with the increase in the temperature because, when the temperature increases the molecules of the solvent gain more kinetic energy. Thus, the molecules move randomly and have greater distance from each other. However, there are a few salts like cerium sulphate, lithium carbonate and sodium carbonate monohydrate, etc. whose solubility decreases with the increase in temperature.
Hence, Cerium sulphate \[\left( {C{e_2}{{\left( {S{O_4}} \right)}_3}} \right)\] is a substance whose solubility is decreases with rise in temperature.
 The substances \[HCl\], \[N{H_3}\], and \[S{O_2}\] have solubility, which decreases as temperature increases. They are all gases at standard pressure. When a solvent with a gas dissolved in it is heated, the kinetic energy of both the solvent and solute increases. Because, when temperature is increased, more energy is given to the system, which is used by the gas molecules to overcome the solvent-gas interactions and break free to move into the gaseous state. So, solubility of a gas in liquid decreases with an increase in temperature.

Note:
Note that the solubility of hardness producing salt in water decreases with the rise of temperature. Example, solubility of \[CaS{O_4}\] in water decreases with increase in temperature. Solubility curve is a graphic representation of the variation with changing temperature of the solubility of a given substance in a given solvent.