Answer to Question #117485 in General Chemistry for Jonathan

Question

6.) 173.6 g of Sucrose is mixed with 900g of H2O at 15°C. At 15°C H2O has a vapor pressure of 12.73 torr. Calculate the vapor pressure of the sucrose / water mixture.
(Sucrose has a molar mass of 342.3 g/mol)

Answer 1

Use Raoults Law

P_solvent = X_solvent × P^o_solvent

X(H₂O) = n(H₂O)/(n(suc)+n(H₂O));

n=m/M;

n(suc) = 173.6 g / 342.3 g/mol = 0.507 moles;

M(H2O) = 18 g/mol;

n(H₂O) = 900 g / 18 g/mol = 50 moles;

X(H₂O) = 50 mol / (0.507 mol + 50 mol) = 0.9899;

P_solvent = 0.9899 × 12.73 torr = 12.6 torr;

Answer: 12.6 torr