What is a saturated solution?

1 Answer
Feb 11, 2016

Answer:

Neither of the previous answers have defined a saturated solution, and would properly be rejected by an examiner. Saturation defines an EQUILIBRIUM condition.

Explanation:

A saturated solution is a solution in which the concentration of the SOLUTE is equal to that concentration that would be in equilibrium with UNDISSOLVED solute. As for any equilibrium we would normally specify a temperature (because at higher temperature, the solvent could probably dissolve more solute).

So for a water soluble salt, #M^(+)X^-#, we could write the following equilibrium reaction:

#M^(+)X^(-)(s) stackrel(H_2O)rightleftharpoons M^(+)(aq) + X^(-)(aq)#.

We would probably also specify a temperature, and we could write the equilibrium condition as : #K_(sp) = [M^(+)(aq)][X^(-)(aq)]# (#sp# stands for #"solubility product"#, and has been measured for many salts). If #K_(sp)# were small, what could you say with respect to the solubility of the salt?

When the ion product (i.e. #[M^(+)(aq)][X^(-)(aq)]# #=# #K_(sp)#, the solution is said to be #"saturated"# with respect to #MX#; when the ion product #># #K_(sp)#, the solution is said to be #"SUPERSATURATED"#, and when the ion product #<# #K_(sp)# the solution is #"UNSATURATED"#.

These definitions are very poorly understood at undergraduate level, and I urge you to consider them and test your understanding. I reiterate that saturation defines an equilibrium condition, that has been measured for many salts at various temperatures.