What is the difference between molarity and molality?

Answer 1

I think that both previous definitions of molarity are a little confusing, because they speak of moles of solute per volume of solvent. I think it is best to define molarity as moles of solute per liter of SOLUTION. That way, if the solute actually contributes to the volume, it is accounted for in molarity.

Molality was defined appropriately by both previous answers.

Answer 2

Both molarity and molality are units of concentration. One is defined in terms of the amount of moles per unit of a solution's quantity (either mass or volume):

1) Molarity = M = mol/L This is defined as the concentration of the solution in terms of moles of solute per unit volume of the solution in liters.

2) Molality = mol/kg This is defined as the concentration of the solution in terms of moles of solute per unit mass of the solvent in kilograms.

Answer 3

In chemistry, these are two concepts that are easily confused as both involve moles.

Molarity is the concentration of a solution calculated by one mole of solute per one liter of solvent.

M = mol/L

Molality is the concentration of a solution calculated by moles of solute per kilogram of solvent.

m = mol/kg