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Ideal solutions

Which of the following statements about the composition of the vapour over an ideal 1: 1 molar mixture of benzene and toluene is correct? Assume that the temperature is constant at 250C. (Given, vapour pressure data at 250C, benzene =12.8kPa, toluene =3.85 kPa


 pBenzene =xBenzene pBenzene °pToluene =xToluene pToluene °

 For an ideal 1:1 molar mixture of benzene and toluene, 

xBenzene =12  and  xToluene =12

pToluene =12  pToluene °=12×3.85kPa=1.925kPa

pBenzene =12pBenzene °=12×12.8kPa=6.4kPa

Thus, the vapour will contain a high percentage of benzene as the partial vapour pressure of benzene is higher as compared to that of toluene.

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