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At 298 K, the vapour pressure of pure benzene, C6H6 is 0.256 bar and the vapourpressure of pure tolueneC6H5CH3 is 0.0925 bar. Two mixtures were prepared as follows:0 7.8 g of C6H6 + 9.2 g of toluene(i) 3.9 g of C6H6 + 13.8 g of tolueneThe following questions are multiple choice questions. Choose the mostappropriate answer:0) The total vapour pressure (bar) of solution 1 is(a)(b)(C)0.1280.1740.198(d)0.258(in Which of the given solutions have higher vapour pressure?(a) I(b)Il(c) Both have equal vapour(d) Cannot bepressurepredicted(ill) Mole fraction of benzene in vapour phase in solution 1 is(a)0.128(b)(c)(d)0.1740.7340.266(iv) Solution I is an example of a/an(a) ideal solution(c) non-ideal solution with negativedeviation(b) non-ideal solution with positive dev(d) can't be predicted |
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Answer» Given, \(P^0_{C_6H_6} = 0.256\) bar \(P^0_{C_7H_8} = 0.0925 \) bar molecular weight of C6H6 = 78 g/mol and molecular weight of C7H8 = 92 g/mol. For Solution - 1 Mole fraction of benzene in solution = \(\cfrac{\frac{7.8}{78}}{\frac{7.8}{78}+ \frac{9.2}{92}}\) \(= \frac{0.1}{0.1 + 0.1}\) \(=\frac12\) \(= 0.5\) ∴ Mole fraction of toluene = 1 - 0.5 = 0.5 For Solution - 2 Mole fraction of benzene = \(\cfrac{\frac{3.9}{78}}{\frac{3.9}{78}+ \frac{13.8}{92}}\) \(= \frac{0.05}{0.05 + 0.15}\) \(= 0.25\) ∴ Mole fraction of toluene = 1 - 0.25 = 0.75 ♦ Total vapour pressure in solution 1 \(P_{total} = (X_{benzene}\times P^0_{benzene}) + (X_{toluene} \times P^0_{toluene})\) \(= 0.5 \times 0.256 + 0.5 \times 0.0925\) \(P_{total} = 0.174\) bar ♦ Total vapour pressure in solution - 2 \(P_2 = 0.25 \times 0.256 + 0.75 \times 0.0925\) \(= 0.133\) bar ♦ Solution (1) has higher vapour pressure than Solution (2). ♦ Mole fraction of benzene in vapour phase in Solution (1). ♦ Mole fraction of benzene in vapour phase in solution (1) \(Y_{benzene} = \frac{X_{benzene}\times P^0_{benzene}}{P_{total}}\) \(= \frac{0.5 \times 0.256}{0.174}\) \(Y_{benzene} = 0.734\) ♦ Solution (1) is an example of a ideal solution because toluene and bezene are much similar in polarity they follow Roult's Law. |
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