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When `1.20g` of sulphur is melted with `15.00g` of naphthalene, the solution freezes at `77.2^(@)C`. What is the moalr mass of this from of sulphur. Data for Napthalene Melting point, m.p `80^(@)C` Freezing point depression constant, `k_(f) = 6.80^(@)Cm^(-1)`A. `180 g mol^(-1)`B. `190 g mol^(-1)`C. `260 g mol^(-1)`D. `450 g mol^(-1)` |
Answer» Correct Answer - B A : Benzene B : Toluene `p = p_(A) + p_(B)` `p = p_(A)^(@) x_(A) + p_(B)^(@) x_(B)` `75 xx (1)/(2) + 22 xx (1)/(2)` `= 37.5 + 11 = 48.5` Mole fraction of benzene in vapour, `y_(A) = (p_(A))/(p) = (37.5)/(48) = 0.78` Similarly, mole fraction of toluene in vapour `y_(B) = 0.22` `:.` The vapour will contain higher precentage of benzene |
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