Question

What do we mean when we speak of sodium chloride reaching a saturation point in aqueous solution?

Answer 1

We can talk of salt reaching a saturation point in water solution, and can represent this by the chemical reaction:

`NaCl(s) rightleftharpoons Na^+(aq) + Cl^(-)(aq)`

Explanation:

The above reaction is an equilibrium, and is reached when `[Na^(+)(aq)]` and `[Cl^(-)(aq)]` achieve equilibrium concentrations for a given temperature (tho' in fact the reaction is quite insensitive to temperature). The `(aq)` label designates the aquated ion, i.e. `[Na^(+)(aq)]` is probably `[Na(OH_2)_6]^(+)`, a sodium ion surrounded by or aquated by 6 or so water molecules.

The above reaction is saturated when the the solution contains an amount of solute equal to that which would be in equilibrium with undissolved solute. So if you see undissolved solute, you know that equilibrium has been reached; and if you decant off the supernatant liquid you have a saturated solution. You will have to qualify your other questions.