The vapour pressure of water at 20 ℃ is 17.54 mm Hg. When 20 g of a non-ionic, substance is dissolved in 100 g of water, the vapour pressure is lowered by 0.30 mm Hg. What is the molecular mass of the substance?

Question

The vapour pressure of water at 20 ℃ is 17.54 mm Hg. When 20 g of a non-ionic, substance is dissolved in 100 g of water, the vapour pressure is lowered by 0.30 mm Hg. What is the molecular mass of the substance?, 200.8 g/mol, 206.88 g/mol, 210.5 g/mol, 215.2 g/mol

MARKS App · Accepted Answer

p ° - p s p ° = X s o l u t e or p ° - p s P s = n N ∴ 0.3 17.24 = 20 M 100 18 { M = m o l a r m a s s o f s o l u t e } ∴ M = 20 × 18 × 17.24 0.3 × 100 = 206.88

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