Question

Calculate the molality of a solution where 0.5 grams of toluene (C7H8) is dissolved in 225 grams of (C6H6). Molecular weight = C7H8=7×12+1×8=92 grams/mole

Answer 1

Solution.

The molality is calculated by: $M = \dfrac{\nu_{solute}}{m_{solvent}};$

$\nu(C_7H_8) = \dfrac{m(C_7H_8)}{M(C_7H_8)};$

$M(C_7H_8) = 92g/mol;$

$\nu(C_7H_8) = \dfrac{0.5g}{92g/mol}=0.0054mol;$

 $\nu_{solute}$ is the number of mole solute, and $m_{solvent}$  is the mass of the solvent in kg.

$m_{solvent}=225g=0.225kg;$

The molality then: $M = \dfrac{0.0054mol}{0.255kg}=0.024mol/kg;$

Answer: M = 0.024mol/kg.