Question

Derive relation between molarity and molality. Calculate molality of $1M$ $HCl$ solution having density $1.5365g/mol$.

Answer 1

$\text{Molarity}=\left(\frac{\text{Number of moles of solute}}{\text{Volume of solution in litres}}\right)$

$\text{while Molality}=\frac{\text{moles of solute}}{\text{weight of solvent in kg}}$

the above two have a relationship as,

$\text{Molality}=\frac{\text{molarity}}{\text{(density of the solution}-\text{molarity})\times \text{molecular weight of solute}}$

Molality of the $1MHCl$ is given by,

$\text{Molality}=\frac{1}{(1.5365g/mol-1)\times 36.46g/mol}$

$\text{Molality}=0.05112$