The mass of a non-volatile solute of molar mass $40 {g mol}^{- 1}$ , which on dissolution in $57 g$ octane to reduces the vapour pressure of octane by 20%, is

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Solution

Relative lowering of vapour pressure(RLVP) is a colligative property given by
$\frac{P^{0} - P_{s}}{P^{0}} = X_{b} = \frac{n_{B}}{n_{A} + n_{B}}$
Here A represents solute, B represent solvent (octane) and all other terms have their ususal meanings.
$R L V P = \frac{n_{B}}{n_{A}} = \frac{P^{0} - P_{s}}{P^{0}} = 0.2$
$= \frac{w_{B} / 40}{57 / 114 + w_{B} / 40} = 0.2$
$∴ w_{B} = 5$

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The mass of a non-volatile solute of molar mass 40 g mol−1, which on dissolution in 57 g octane to reduces the vapour pressure of octane by 20%, is

Relative lowering of vapour pressure(RLVP) is a colligative property given by P0−PsP0=Xb=nBnA+nB Here A represents solute, B represent solvent (octane) and all other terms have their ususal meanings. RLVP=nBnA=P0−PsP0=0.2 =wB/4057/114+wB/40=0.2 ∴wB=5

The mass of a non-volatile solute of molar mass $40 {g mol}^{- 1}$ , which on dissolution in $57 g$ octane to reduces the vapour pressure of octane by 20%, is