Question

$BaCl_{2}$ solution has a density of 1.279 g/mL and the percent of solute is 26%. Calculate the molality of the solution? (Mol. Weight of $BaCl_{2}$ = 208)

Answer 1

Let’s calculate the mass of $BaC{ l }_{ 2 }$ and mass of water in the solution

From the given,

Density of the solution = 1.279 g/ml

Density of the solution is calculated by the following formula.

$Density\quad =\quad \frac { Mass\quad of\quad solution }{ volume\quad of\quad solution }$

From the above formula, density is in g/ml and percentage of solute is given ,therefore, volume of the solution is 100 mL.

$1.279\quad g/ml\quad =\quad \frac { Mass\quad of\quad solution }{ 100\quad ml } \\ \\Mass\quad of\quad solution\quad in\quad gram\quad =\quad 127.9\quad g$

Therefore, mass of solute in given 26% of solution

=$\frac { 26 }{ 100 } \times127.9\quad =\quad 33.254g$

Hence,$\quad solvent\quad mass\quad will\quad be\quad =\quad 127.9\quad -\quad 33.254\quad =\quad 94.646g$

$Molarity\quad of\quad solution\quad =\quad \frac { Weight\quad of\quad solute\quad \times \quad 1000 }{ Molecular\quad weight\quad \times \quad Weight\quad of\quad solvent\quad in\quad grams } \\\\ \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad =\quad \frac { 33.254\quad \times \quad 1000 }{ 208\quad \times 94.646 } \quad =\quad 1.689\quad m$

Molarity of the solution is 1.689 m.