Answer to Question #141774 in General Chemistry for gia

Question

Safrole is contained in oil of sassafras and was once used to flavor root beer. A 2.39-mg sample of safrole was dissolved in 103.0 mg of diphenyl ether. The solution had a melting point of 25.70°C. Calculate the molecular mass of safrole. The freezing point of pure diphenyl ether is 26.84°C, and the freezing-point depression constant, Kf, is 8.00°C/m.

Answer 1

∆T=K_fC_m, where C_m is the molality of the solution.

∆T=T₀-T_f=26.84-25.7=1.14°C,

C_m=∆T/K_f=1.14/8.00=0.1425(mol/kg),

C_m=n_solute/m_solvent

n_solute=C_m•m_solvent=0.1425×0.000103=0.0000147(mol)

M=m/n=0.00239/0.0000147=162.59(g/mol)