Question

What are units of molality and molarity?

Answer 1

The molality is referred to the moles of a solute with respect to the mass of a solvent, while the molarity describes the moles of a solute in relation to the volume of a solution.

Complete step by step solution:
Both molarity and molality are used to measure concentration of a chemical solution.
Firstly, it is important to clear that $solution=solute+solvent$ .
Molality(m) is the amount of a solute dissolved in a certain mass of solvent, also called molal concentration. It is defined as the number of moles of a solute per kilogram of a solvent.
$molality(m)=\dfrac{{{n}_{solute}}}{{{w}_{solvent}}}$
Where ${{n}_{solute}}=$ number of moles of solute added
${{w}_{solvent}}=$ mass of solvent in kilograms
Therefore , the units of molality is mol/kg or $mol.k{{g}^{-1}}$ .
Molarity (M) is the amount of a substance added in a certain volume of solution. Molarity is defined as the number of moles of a solute added in a solution per liter of solution. Molarity can also be called as the molar concentration of a solution.
$Molarity(M)=\dfrac{{{n}_{solute}}}{{{V}_{solution}}}$
Where, ${{n}_{solute}}=$ number of moles of solute added
${{V}_{solution}}=$ volume of solution in liters.
Therefore, the units of molarity is mol/L or $mol.{{L}^{-1}}$ .

Note: Molarity(M) and molality(m) should not be confused with Normality(N). Normality is also used to measure concentration of chemical solution but it is defined as the number of gram equivalents of solute present in one litre of a solution.