The vapor pressure of pure water at 10C is 9.2 torr. How many grams of MgCl2 would you need to add to 500 mL of water to drop the vapor pressure to 8.0?

Answer 1

delta P = i*X_solute*P^o
delta P is 9.2-8.0 = >
Po = 9.2
i = 3 for MgCl2.
Solve for X_solute and use nsolute/(nsolute+nsolvent) = X
(Note that n solvent is 500/18). Solve for nsolute, convert to grams MgCl2.