Molarity vs. Molality: How to Calculate and What They Mean

Molality and molarity are both ways to measure how concentrated a chemical fluid is. To put it simply, the main difference is between mass and volume.

The molarity tells you how many moles of a solute there are in a solution based on its volume, while the molality tells you how many moles of a liquid there are based on its mass.

Read on to find out more about molarity and molality, including how to use them, what they mean, and how they compare to each other.

What Does Molality Mean?

If you know how much of a material dissolves in a certain mass of solvent, you know its molality (m). It is the number of moles of a solute in kilogrammes of a liquid. Last changed on May 4, 2020.

Units and formula for molality

A mole is equal to mol/kg or m^2.

Formula for molality

m = moles of solute/kilograms of solvent

What Does Molarity Mean?

Molarity, or M, is the amount of a material that can be found in a certain amount of solution. Molarity is the number of moles of a solute in one litre of a solution. It’s also possible to talk about a solution’s molar concentration.

Units and the formula for molarity

Molarity is measured in units of M or mol/L. A solution with 1 M is called “one molar.”

Formula for molarity

I = moles of solute / litres of solution

Different types of molality

A solution is not the same as a liquid, which is an important difference between molality and molarity.

The number of moles of a solute to the total number of litres of a solution is called its molarity. The solute and the liquid are both in the solution.

When you compare the moles of a solute to the kilogrammes of a liquid, you get the moality. Keep in mind that the mass used in the base is only that of the solvent and not of both the solute and the solvent.