What are some common mistakes students make with points of saturation?

1 Answer
Oct 21, 2015

Saturation is an equilibrium concept; IT DOES NOT MEAN that the solvent holds all the solute that it can.


When we say a solvent is saturated with solute, we usually specify a temperature, because a hot solution can hold more solute than a cold one. When a common solute is dissolved to saturation point, we mean that the solvent holds the same amount of solute that would be equilibrium with undissolved solute. So for #Na_2SO_4# dissolved in water, we could write the equation:

#Na_2SO_4(s) rightleftharpoons 2Na^+ + SO_4^(2-)#

As for any equilibrium we could write the equation,

#K_(sp) = [Na^+]^2[SO_4^(2-)]#. #K_(sp)# is simply a number, which may be large or small, and has been extensively measured for a range of sparingly soluble inorganic salts in water. At this saturation point, addition of any further sodium or sulfate ion would result in the precipitation of sodium sulfate.

The #sp# subscript stands for "solubility product". If I have gone off the track, would you please respecify your question?