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CBSE Class 12-science Answered

2g of a substance dissolved in 40g of water produced a depression of 274.5K in the freezing point of water. Calculate the molecular mass of the substance .The molal depression constant for water is 274.85K per molal
Asked by mukundsharma70 | 05 Aug, 2019, 10:50: PM
answered-by-expert Expert Answer
Given:
 
Mass of solute, w2= 2 gm
 
Mass of solvent, w1 = 40 gm
 
Depression in freezing point = 274.85 - 274.5
 
                                         =0.35 K
 
Freezing point depression constant Kf = 1.86 K. kg/mol
 
Molecular mass of solute can be calculated by using formula,
 
straight M subscript 2 space equals space fraction numerator straight K subscript straight f cross times straight w subscript 2 cross times 1000 over denominator increment straight T subscript straight f cross times straight w subscript 1 end fraction

space space space space space equals fraction numerator 1.85 cross times 2 cross times 1000 over denominator 0.35 cross times 40 end fraction

straight M subscript 2 space equals 265.71 space straight g divided by mol
 
 
Molecular mass of the substance is 265.71 g/mol
 
 
 
Answered by Varsha | 06 Aug, 2019, 10:36: AM
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