Question

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

Answer 1

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

Explanation:

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?