1. The problem statement, all variables and given/known data Some KCl is dissolved in water at 25°C, where it completely dissociates. The vapor pressure of pure water at 25°C is 28.3 mmHg. Estimate the mass in grams of KCl needed per liter of pure water to reduce the vapor pressure of water at 25°C by 5%. 2. Relevant equations 3. The attempt at a solution I'm really not sure how to go about this problem. First I thought I could maybe use raoult's law, but then I don't think that would work to get the mass of the solute. Then I thought maybe if the vapor pressure is lowered by 5%, then the solvent is also lowered by 5%, which would mean that for 1 L of water I would need 0.05 L of KCl to lower the vapor pressure by 5%, but I don't think this is right either.