# What is the difference between the concentration terms of "molarity", and "molality"?

Jul 3, 2017

#### Answer:

At low concentrations they are equivalent.........

#### Explanation:

As you know, we define these concentrations as:

$\text{Molarity"="Moles of solute"/"Volume of solution}$, and thus molarity typically has the units of $m o l \cdot {L}^{-} 1$.

On t'other hand.........

$\text{Molality"="Moles of solute"/"Mass of solution (kg)}$, and thus molality typically has the units of $m o l \cdot k {g}^{-} 1$.

To make the conversion, we would typically require the $\text{density}$ of the solution, ${\rho}_{\text{solution}}$...........so that we can assess the volume of the solution...........

See here for a model calculation.