question_answer 8)

The density of 3M solution of \[\text{NaCl}\] is \[1.25g\,m{{L}^{-1}}\]Calculate the molality of solution.

Answer:

Let volume of solution = 1 litre, i.e., 1000 mL Mass of solution \[=1000\times 1.25=1250\text{ }g\] Mass of solute dissolved \[=3\times 58.5=175.5\text{ }g\] Mass of solvent \[=1250-175.5=1074.5\text{ }g\] Molality \[(m)=\frac{{{w}_{B}}\times 1000}{{{m}_{B}}\times {{w}_{A}}}\] \[=\frac{175.5\times 1000}{58.5\times 1074.5}=2.79\]