Expressions of Concentration

There are general terms and very specific terms used to express the concentration of a solution. The general terms and their definitions are:

Dilute: small amount of solute is dispersed in the solvent.

Concentrated: large amount of solute is dissolved in the solvent.

Saturated: the solution is holding all the solute possible at that temperature. This is not a static condition; that is, some solute particles are exchanging places with some of the undissolved particles, but the total solute in solution remains the same. This is an example of equilibrium.

Unsaturated: more solute can go into solution at that temperature. The solvent has further capacity to hold more solute.

Supersaturated: sometimes a saturated solution at a higher temperature can be carefully cooled so that the solute does not get a chance to come out of solution. At a lower temperature, then, the solution will be holding more solute in a solution than it should for saturation and is said to be supersaturated. As soon as the solute particles are jarred or a "seed" particle is added to the solution to act as a nucleus, they rapidly come out of solution so that the solution reverts to the saturated state.

Molarity

Molarity (abbreviated M) is defined as the number of moles of a substance dissolved in 1 liter of solution.

A 1 molar H2SO4 solution would have 98 grams of H2SO4 (its molar mass) in 1 liter of solution.

Molality

Molality (abbreviated m) is defined as the number of moles of the solute dissolved in 1000 grams of solvent.

A 1 molal solution of H2SO4 would have 98 grams of H2SO4 dissolved in 1000 grams of water. This, you will notice, gives a total volume greater than 1 liter, whereas the molar solution had 98 grams in 1 liter of solution.