Elements P and Q form two types of non-volatile, non-ionizable compounds PQ and PQ2. When 1 g of PQ is dissolved in 50 g of solvent ‘A’. Tb was 1.176 K while when 1 g of PQ2 is dissolved in 50 g of so

Question

Elements P and Q form two types of non-volatile, non-ionizable compounds PQ and PQ2. When 1 g of PQ is dissolved in 50 g of solvent ‘A’. Tb was 1.176 K while when 1 g of PQ2 is dissolved in 50 g of solvent ‘A’, Tb was 0.689 K. (Kb of ‘A’ = 5 K kg mol –1). The molar masses of elements P and Q (in g mol –1) respectively, are :

(A) 70, 110
(B) 65, 145
(C) 60, 25
(D) 25, 60

Prashant Kotian · Accepted Answer

Correct answer: D. (Tb)PQ = Kbm 1 1.176 M   M1 = 85.03   b PQ 1 T M    = 0.689 M2 = 145.13 Let molar mass of P & Q are MP and MQ respectively MP + MQ = 85.03 MP + 2MQ = 145.13 MP = 24.93  25 MQ = 60.1  60

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