At T(K), 2 moles of liquid A and 3 moles of liquid B are mixed. The vapour pressure of ideal solution formed is 320 mm Hg. At this stage, one mole of A and one mole of B are added to the solution. The vapour pressure is

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Quantrex Academy · Accepted Answer

Correct answer: D. 500, 200

For an ideal solution obeying Raoult's Law, total pressure is

P = P_A^o x_A + P_B^o x_B

.
Initially with 2 moles A and 3 moles B:

x_A = 0.4, x_B = 0.6

, and

P = 320 = 0.4P_A^o + 0.6P_B^o

After adding 1 mole each: 3 moles A and 4 moles B gives

x_A = \frac{3}{7}, x_B = \frac{4}{7}

, and

P = 328.6 = \frac{3}{7}P_A^o + \frac{4}{7}P_B^o

From the first equation:

3200 = 4P_A^o + 6P_B^o

From the second:

2300.2 = 3P_A^o + 4P_B^o

Solving: We find

P_B^o = 200

mm Hg and

P_A^o = 500

mm Hg.

At T(K), 2 moles of liquid A and 3 moles of liquid B are mixed. The...

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