Page 81 - Chemistry ICSE Class IX
P. 81
Water 69
Solubility
What is meant by solubility
Solubility of a substance is de ned as follows: Mass of the solute in grams
which dissolves in 100 g of solvent to form a saturated solution at any
temperature is called its solubility at that temperature. For example, 100 g
of water at 25°C can dissolve 36.5 g of sodium chloride to obtain a saturated
solution. So, the solubility of sodium chloride at 25°C is 36.5 g per 100 g of
water.
If w g of a solute dissolves in W g of a solvent to obtain a saturated
solution at any particular temperature and pressure, then
w g
Solubility of the solute = × 100 g per 100 g of solvent
W g
The solubility depends on the following factors:
Temperature. The solubility of solid solutes in liquids usually increases
with a rise in temperature and decreases with a fall in temperature.
However, there are a few exceptions. For example,
Solubility of slakedlime in water decreases with a rise in temperature.
Solubility of calcium sulphate in water increases with a rise in
temperature from 0°C to 40°C and decreases thereafter.
The solubility of a gas in a liquid usually decreases with a rise in
temperature.
Fig. 3.8 A gas dissolves in a liquid and
Pressure. Pressure has a very little effect on the solubility of solids in an equilibrium, Gas U Gas in solution,
liquids. However, the solubility of a gas in a liquid increases with an is established
increase in the pressure of the gas.
Nature of solute and solvent. Polar and ionic compounds dissolve
more in polar solvents. For example, the solubility of polar compounds
which can form hydrogen bonds with water is usually much higher.
Effect of Temperature and Pressure on the Solubility
The effect of temperature and pressure on the solubility of any substance
depends upon the nature of solute and solvent.
What is the effect of temperature and pressure on the
solubility of a gas in a liquid
Gases dissolve in liquids. The solubility of a gas in any liquid depends upon:
Nature of the gas and that of the liquid
Temperature of the liquid
Pressure of the gas over the surface of the solution.
Gases, such as ammonia (NH ) and hydrogen chloride (HCl), are highly
3
soluble in water. Carbon dioxide (CO ) and oxygen (O ) also dissolve to
2
2
some extent. Gases, such as helium and nitrogen, have very little solubility
in water.
The solubility of a gas in a liquid
Decreases with a rise in the temperature
Increases with an increase in the pressure of the gas
