The
water-solubility of gases varies widely and, as the graphs show,
decreases with temperature.
The
atmospheric gases (oxygen and nitrogen) have
low water-solubility (
less than 0.005 g per 100 g water at 20 °C).
You will have seen bubbles appearing in water being heated long before it boils.The bubbles at temperatures below the boiling point are oxygen which is escaping from the solution due to its lower solubility at the higher temperature.
Do not however forget, that by the time the water reaches its boiling point, all of the oxygen is gone, and the bubbles appearing at this point are water vapour.Carbon dioxide (the gas in fizzy drinks) has
moderate water solubility (
4 g per 100 g water at 20 °C).
Ammonia and
hydrogen chloride have high solubility (
up to 70 g per 100 g water at 20 °C). These are commonly found in laboratories in aqueous solutions referred to as hydrochloric acid and ammonia.
The temperature-dependence of the solubility of gases in water is of great consequence for aquatic life because fish and aquatic plants need oxygen to survive.
Thermal pollution which increases the temperature of the water also accelerates the rate of metabolism for fish.
This increases their oxygen requirement at the same time as the oxygen solubility decreases due to the higher temperature.
**The significant water-solubility of HCl gas even at 0 °C is due to its reaction with water to form the ions H3O+ and Cl– (which is why an aqueous solution of hydrogen chloride is known as hydrochloric acid).