The vapour pressure of a solution having 2.0 g of solute X (molar atomic mass = 32 g mol–1) in 100 g of CS2 (vapour pressure = 854 torr) is 848.9 torr. The molecular formula of the solute is:-



(1) X
(2) X2
(3) X4
(4) X8
Kindly answer sir/mam.


According to lowering of vapour pressure,P0-PP0 = W2W1 × M1M2P0 - vapour pressure of pure solvent = 854 torrP -vapour pressure of solution = 848.9 torr.W2 - weight of the solute = 2 gW1 - weight of the solvent = 100 gM2 - molecular mass of the solute = ?M1 - molecular mass of the solvent CS2= 12 + 2 × 32 = 12 + 64 = 76 g854 - 848.9854 = 2100 × 76M2M2 = 2 × 76 × 854100 × (854 - 848.9) = 254.5 gMolecular weight of the solute  = X × nWhere X = atomic mass = 32X × n = 254.5n = 254.5X = 254.532 =7.95Thus the formula of the solute = X8

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