Question

the boiling point of benzene is 353.23 k. when 1.80 g of a non-volatile solute was dissolved in 90 g of benzene, the boiling point is raised to 354.11 k. calculate the molar mass of the solute. kb for benzene is 2.53 k kg mol-1.

Answer 1

The molar mass of the non-volatile solute was calculated using the change in boiling point due to the solute, the mass of the solvent, and the boiling point elevation constant for benzene. The final molar mass was determined to be 57.51 g/mol.

Step-by-step explanation:

To calculate the molar mass of the solute, we first determine the change in boiling point, ΔTb, caused by the solute. The change in boiling point ΔTb is the difference between the boiling point of the solution and the boiling point of the pure solvent, which is ΔTb = 354.11 K - 353.23 K = 0.88 K. Next, we calculate the molality (m) of the solution using ΔTb and the boiling point elevation constant (Kb) for benzene:

m = ΔTb / Kb = 0.88 K / (2.53 K kg/mol) = 0.347826 mol/kg

Since we have the mass of the solvent (benzene) and the molality, we can determine the number of moles of solute:

Number of moles = molality (m) × mass of solvent (kg) = 0.347826 mol/kg × 0.09 kg = 0.031304 mol

Finally, we calculate the molar mass (M) by dividing the mass of the solute by the number of moles:

M = mass of solute / number of moles = 1.80 g / 0.031304 mol = 57.51 g/mol

Therefore, the molar mass of the solute is 57.51 g/mol.