GATE 2023 CY – Question 63

Physical Chemistry · Solutions: Ideal and non-ideal solutions, Raoult’s Law and Henry’s Law. · 2 marks · Numerical answer

Dissolve 128 g naphthalene ($C_{10}H_8$) in 780 g benzene ($C_6H_6$). Pure-benzene vapour pressure is 12.6 kPa at 25 °C. For an ideal solution, benzene partial vapour pressure is ______ kPa (two decimal places).

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Correct answer: 11.34 to 11.47

Explanation

Moles naphthalene=128/128=1 and benzene=780/78=10. Solvent mole fraction=10/11. Raoult law gives pbenzene=(10/11)12.6=11.454545 kPa, rounded **11.45 kPa**. Naphthalene is the nonvolatile solute in the stated ideal model.