How many grams of sucrose must be added to 320 g of water to lower the vapor pressure by `1.5 mmHg`
Channel: Doubtnut
Date: 2020-08-30

How many grams of sucrose must be added to 320 g of water to lower the vapor pressure by `1.5 mmHg` at `25^(@)C`? The vapor pressure of water is 23.8 mmHg and the molar mass of sucrose is `342 g mol^(-1)`. Strategy: If the solute like sucrose is nonvolatile, the vapor pressure of the solution is entirely due to the vapor pressure of the solvent, `P_("solution")=P_("solvent")`. According to Raoult's law, `P_("soln")=P_("solv")^(0) chi_("solv")`, which can be rearranged to the form `chi_("solv")=P_("soln")//P_("solv")^(0)`. This equation can then be solved to find the number of moles of sucrose and hence the grams.