(vii) The vapour pressure of pure water at \( 25^{\circ} C \) is \( 18 mm Hg \). When a nonelectrolyte is dissolved, its vapour pressure becomes \( 17.32 mm Hg \). What is the relative lowering of vapour pressure of the solution?


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We have given,

The vapour pressure of pure water at 25°C = 18mm Hg.

After addition of non-electrolyte, the vapour pressure of water = 17.32 mm Hg.

Then,

lowering in vapour pressure = (18 - 17.32) mm Hg. = 0.68 mm Hg.

∴ relative lowering in vapour pressure \(=\frac{0.68\,mmHg}{18.0\,mmHg}=0.038\)