5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 torr respectively. Which of the following is true regarding the described solution? [202

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Q.
5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 torr respectively. Which of the following is true regarding the described solution [2025]

1 The solution is ideal.

2 The solution has volume greater than the sum of individual volumes.

3 The solution shows positive deviation.

4 The solution shows negative deviation.

Ans.
(4)

Given: $n_{X} = 5, n_{Y} = 10$

$x_{X} = \frac{5}{5 + 10} = \frac{5}{15} = \frac{1}{3}$

$x_{Y} = \frac{10}{5 + 10} = \frac{10}{15} = \frac{2}{3}$

Given: $p_{total} = 70$ $torr$

$p_{X}^{°} = 63$ $torr, p_{Y}^{°} = 78$ $torr$

$p = p_{X} + p_{Y} = \frac{1}{3} \times 63 + \frac{2}{3} \times 78 = 73$ $torr$

Vapour pressure of solution i.e., 70 torr is less than that predicted by Raoult's law. Hence, it shows negative deviation.

Solution

Q.
5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 torr respectively. Which of the following is true regarding the described solution [2025]

1 The solution is ideal.

2 The solution has volume greater than the sum of individual volumes.

3 The solution shows positive deviation.

4 The solution shows negative deviation.

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Solution

Q. 5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 torr respectively. Which of the following is true regarding the described solution [2025]

1 The solution is ideal.

2 The solution has volume greater than the sum of individual volumes.

3 The solution shows positive deviation.

4 The solution shows negative deviation.

Ans. (4) Given: nX=5, nY=10 xX=55+10=515=13 xY=105+10=1015=23 Given: ptotal=70 torr pX°=63 torr, pY°=78 torr p=pX+pY=13×63+23×78=73 torr Vapour pressure of solution i.e., 70 torr is less than that predicted by Raoult's law. Hence, it shows negative deviation.

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Q.
5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 torr respectively. Which of the following is true regarding the described solution [2025]