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Two elements A and B form compounds having formula AB_2 and AB_4 . When dissolved in20 g of benzene (C_6H_6), 1 g of AB_2lowers the freezing point by 2.3 K whereas 1.0 g of AB_4lowers it by 1.3 K. The molar depression constant for benzene is 5.1 K kg "mol"^(-1) . Calculate atomic masses of A and B. |
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Answer» SOLUTION : Using the formula, `M_2 = (1000K_f w_2)/(w_1 XX DELTA T_f)` Molar MASS of `AB_2 , M_(AB_2) = (1000xx 5.1 xx 1)/(20 xx 2.3) = 110.87 g "mol"^(-1)` Molar mass of`AB_4 , M_(AB_4) = (1000 xx 5.1 xx 1)/(20 xx 1.3) = 19615 g "mol"^(-1)` Atomic mass of A + 2 (Atomic mass of B) = 110.87....(i) Atomic mass of A + 4 (Atomic mass of B) = 196.15...(ii) Equation (ii) - Equation (i) gives 2 (Atomic mass of B) = 85.28 orAtomic mass of B = 42.64 u Substituting in equation (i), we get Atomic mass of A + 85.28 = 110.87 Atomic mass of A = 25.59 u. |
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