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explain why the lower vapor pressure for a solution containing nonvolatile solut

ID: 994169 • Letter: E

Question

explain why the lower vapor pressure for a solution containing nonvolatile solute results in a higher boiling point and lower melting point compare to the pure solvent explain why the lower vapor pressure for a solution containing nonvolatile solute results in a higher boiling point and lower melting point compare to the pure solvent explain why the lower vapor pressure for a solution containing nonvolatile solute results in a higher boiling point and lower melting point compare to the pure solvent

Explanation / Answer

When a solute is added to a solvent, the vapor pressure of the solvent (above the resulting solution) is lower than the vapor pressure above the pure solvent.

The vapor pressure of the solvent above a solution changes as the concentration of the solute in the solution changes (but it does not depend on the identity of either the solvent or the solute(s) particles (kind, size or charge) in the solution).

Non-Volatile Solutes

Experimentally, we know that the vapor pressure of the solvent above a solution containing a non-volatile solute (i.e., a solute that does not have a vapor pressure of its own) is directly proportional to the mole fraction of solvent in the solution. This behavior is summed up in Raoult's Law:

Psolvent = XsolventPosolvent

where:

        Psolvent is the vapor pressure of the solvent above the solution,
        Xsolvent is the mole fraction of the solvent in the solution, and
        Posolvent is the vapor pressure of the pure solvent.

Note that