JEE Main 2022 · 27 Jul · Shift 2 · Chemistry Q84

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ChemistryInteger+4 / -1Question 84 of 90

When a certain amount of solid A is dissolved in 100 g of water at 25°C to make a dilute solution, the vapour pressure of the solution is reduced to one-half of that of pure water. The vapour pressure of pure water is 23.76 mmHg. The number of moles of solute A added is ______. (Nearest Integer)

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Answer and worked solution

Official answer: 3

Raoult's law for a dilute solution: $\frac{\Delta p}{p^\circ}\approx\frac{n_A}{n_{water}}$ . So $\frac12=\frac{n_A}{100/18}$ and $n_A\approx2.8\approx3$ .

Answer: 3

Topics:Raoult's law and vapour pressure Colligative properties

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JEE Main 2022 · 27 Jul · Shift 2, Chemistry question 84