'A' tetramerises in water upto $ 80 \% $. A solution of $ 2.5 \mathrm{~g} $ of $ \mathrm{A} $ in $ 100 \mathrm{~g} $ of water lowers the freezing point by $ 0.3^{\circ} \mathrm{C} $. The molar mass of $ \mathrm{A} $ is $ \left(\mathrm{K}_{\mathrm{f}}\right. $ for $ \mathrm{H}_{2} \mathrm{O} $ is $ \left.1.86\right) $

Question

'A' tetramerises in water upto $ 80 \% $. A solution of $ 2.5 \mathrm{~g} $ of $ \mathrm{A} $ in $ 100 \mathrm{~g} $ of water lowers the freezing point by $ 0.3^{\circ} \mathrm{C} $. The molar mass of $ \mathrm{A} $ is $ \left(\mathrm{K}_{\mathrm{f}}\right. $ for $ \mathrm{H}_{2} \mathrm{O} $ is $ \left.1.86\right) $, $ 31 $, $ 62 $, $ 122 $, $ 244 $

MARKS App · Accepted Answer

α = 1 - i 1 - 1 n 0 .8 = 1 - i 1 - 1 4 i = 0 .4 ∵ ∆ T = i × k f × m 0 .3 = 0 .4 × 1 .86 × w A × 1000 M A × w H 2 O 0.3 = 0.4 × 1.86 × 2.5 × 1000 M A × 100 M A = 0.4 × 1.86 × 2.5 × 1000 0.3 × 100 = 62 u

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