Retorts

Salt Solution

I write to you about the letter of Geoff Wyvill on salt solubility [June].

While he is technically correct that sodium chloride solubility increases with temperature, the change is so small that most teachers of senior chemistry would teach it as an example of a material that changes little with temperature (cf Ca(OH)₂ which decreases; KNO₃ which increases).

What he is describing in his experiment is the rate of dissolving which, like all chemical reactions, increases with increasing temperature. The solubility equilibrium is reached much faster at a higher temperature.

When you insist on checking things by experiment, you must be sure of what you are measuring.

Hal Morgan, HOD Science, The Correspondence School