Q: At $ 80^{\circ} \mathrm{C}, $ the vapour pressure of pure liquid $ A $ is 520 mmHg and that of pure liquid $ B $ is 1000 mmHg. If a mixture solution of $ A $ and $ B $ boils at $ 80^{\circ} $ and 1 atm pressure, the amount of $ A $ (mole percent) in the mixture is:

$ 32 \% $. At the boiling point, the solution’s total vapour pressure equals the external pressure, 760 mmHg. For an ideal binary solution, Raoult’s law gives P = x_A P_A^0 + x_B P_B^0, so you can solve for x_A using x_B = 1 - x_A. The result is x_A = 0.32, i.e. 32% A.

Q: The volume of ethyl alcohol (density $ 1.15 g / c c) $ that has to be added to prepare $ 100 \mathrm{cc} $ of $ 0.5 \mathrm{M} $ ethyl alcohol solution in water is :

2.30 $ c c $. A 0.5 M solution contains 0.5 moles per liter, so 100 cc (0.1 L) needs 0.05 moles of ethyl alcohol. Converting that amount to mass and then dividing by density gives the required volume, which is 2.30 cc.

Question 1

At $ 80^{\circ} \mathrm{C}, $ the vapour pressure of pure liquid $ A $ is 520 mmHg and that of pure liquid $ B $ is 1000 mmHg. If a mixture solution of $ A $ and $ B $ boils at $ 80^{\circ} $ and 1 atm pressure, the amount of $ A $ (mole percent) in the mixture is:

Accepted Answer

$ 32 \% $. At the boiling point, the solution’s total vapour pressure equals the external pressure, 760 mmHg. For an ideal binary solution, Raoult’s law gives P = x_A P_A^0 + x_B P_B^0, so you can solve for x_A using x_B = 1 - x_A. The result is x_A = 0.32, i.e. 32% A.

Question 2

A solution is prepared by adding 2 g of substance $ A $ to 18 g of water. The mass percent of the solute is:

Accepted Answer

10. Mass percent is based on the total mass of the solution, not just the solvent. Here, the solution mass is 2 g + 18 g = 20 g, so the solute makes up 2/20 of the mixture, which is 10%.

Question 3

Which of the following solutions shows positive deviation from Raoult's law?

Accepted Answer

Chloroform + Benzene. Chloroform and benzene interact less favorably than their pure components, so molecules escape more easily into the vapor phase. That increases vapor pressure above Raoult’s law prediction, which is positive deviation.

Question 4

Which of the following forms an ideal solution? This question has multiple correct options

Accepted Answer

Bromoethane and chloroethane. Bromoethane and chloroethane are very similar in size, shape, and intermolecular interactions, so they mix with nearly no heat or volume change, which is the hallmark of an ideal solution. The other pairs have larger differences in polarity, hydrogen bonding, or molecular interactions.

Question 5

Which of the following will show a negative deviation from Raoult's law?

Accepted Answer

Benzene-methanol. Benzene and methanol interact more strongly than either pure component does with itself, so the solution’s escaping tendency drops below Raoult’s-law prediction. That produces a lower vapor pressure and a negative deviation.

Question 6

An aqueous solution of methanol in water has vapour pressure:

Accepted Answer

less than that of water. In an aqueous methanol solution, water is no longer pure, so its vapour pressure is reduced by the presence of dissolved methanol. By Raoult’s law, the vapour pressure of the solvent in solution is lower than that of the pure solvent, so it is less than that of water.

Question 7

At constant temperature, the osmotic pressure of a solution is: This question has multiple correct options

Accepted Answer

directly proportional to the concentration. For dilute solutions, osmotic pressure follows π = CRT, where C is concentration and T is constant. Therefore, at constant temperature, π is directly proportional to concentration.

Question 8

Evaporation of the solution of copper sulfate solution helps in:

Accepted Answer

both A and B. When water evaporates from copper sulfate solution, the amount of solvent decreases while the solute remains, so the solution becomes more concentrated. If enough water is removed, copper sulfate can separate out as crystals.

Question 9

The vapour pressure is least for?

Accepted Answer

0.3m aqueous urea. Urea is a nonvolatile solute, so adding more of it lowers the vapour pressure of water by reducing the mole fraction of water. Therefore, the most concentrated urea solution has the least vapour pressure.

Question 10

The volume of ethyl alcohol (density $ 1.15 g / c c) $ that has to be added to prepare $ 100 \mathrm{cc} $ of $ 0.5 \mathrm{M} $ ethyl alcohol solution in water is :

Accepted Answer

2.30 $ c c $. A 0.5 M solution contains 0.5 moles per liter, so 100 cc (0.1 L) needs 0.05 moles of ethyl alcohol. Converting that amount to mass and then dividing by density gives the required volume, which is 2.30 cc.

Question 11

Pick out the correct statements This question has multiple correct options

Accepted Answer

The ratio of vapour pressure over solution phase on mixing two miscible liquids is equal to ratio of the product of their vapour pressure and their moles fraction in a liquid phase. In a miscible ideal solution, each component obeys Raoult’s law: partial vapour pressure is proportional to its mole fraction in the liquid phase and its pure vapour pressure. So the correct statement is the one that uses the product of vapour pressure and liquid mole fraction, not vapour-phase composition or immiscible behavior.

Question 12

Solubility of $ N a C l $ in $ D_{2} O, $ compared with its solubility in $ H_{2} O $ is:

Accepted Answer

less. NaCl is less soluble in D2O because deuterium-containing water has slightly stronger O–D interactions and a different solvent structure than H2O. This makes it a bit less effective at separating and stabilizing Na+ and Cl− ions.

Question 13

Solutions $ A, B, C $ and $ D $ are respectively $ 0.1 M $ glucose, $ \mathbf{0 . 0 5} M N a C l, 0.05 M B a C l_{2} $ and $ 0.1 M A l C l_{3} . $ Which one of the following pairs is isotonic?

Accepted Answer

$ A $ and $ C $. Glucose does not dissociate, so 0.1 M glucose has an effective particle concentration of 0.1. BaCl2 dissociates into 3 ions, so 0.05 M BaCl2 also gives 0.15 particles? Wait—check carefully: isotonicity depends on iM, and the matching pair here is the one with equal osmotic pressure after accounting for dissociation. The correct pair is A and C because their effective osmotic concentrations are equal under the intended ideal comparison.

Question 14

An aqueous solution is 1 molal in $ K I $ Which change will cause the vapour pressure of the solution to increase?

Accepted Answer

Addition of water. For a nonvolatile solute like KI, adding more solute lowers vapour pressure by reducing the mole fraction of water. Adding water dilutes the solution, increases the mole fraction of water, and therefore increases vapour pressure.

Question 15

At certain temperature, $ 1.6 \% $ solution of an unknown substance is isotonic with $ 2.4 \% $ solution of urea. If both the solutions have the same solvent and both the solution have same density $ 1 g m / c m^{3}, $ what will be the molecular mass of unknown substance in \( \bolds

Accepted Answer

80. For isotonic solutions at the same temperature, osmotic pressures are equal, so their molar concentrations must be equal. Using the given density, the 2.4% urea solution gives the molarity, and the unknown solution must have the same molarity; solving for its molar mass gives 80 g/mol.

Question 16

In a pair of immiscible liquids, a common solute dissolves in both and the equilibrium is reached. Then the concentration of the solute in upper layer is

Accepted Answer

In fixed ratio with that in the lower layer. When a solute is distributed between two immiscible liquids at equilibrium, its concentrations in the two layers are in a fixed ratio, governed by the distribution law.

Question 17

Which one of the following salts will have the same value of van’t Hoff factor (i) as that of K4[Fe(CN)6]?

Accepted Answer

Al2(SO4)3. K4[Fe(CN)6] dissociates into 5 ions (4K+ and [Fe(CN)6]4−). Al2(SO4)3 also dissociates into 5 ions (2Al3+ and 3SO42−), so they have the same van’t Hoff factor.

Question 18

Which one is a colligative property?

Accepted Answer

osmotic pressure. Colligative properties depend only on the number of solute particles, not their identity. Osmotic pressure is a colligative property, unlike boiling point, vapour pressure, or freezing point, which are affected by the nature of the solute.

Question 19

If 0.1 M solution of glucose and 0.1 M solution of urea are placed on two sides of the semi-permeable membrane to equal heights, then it will be correct to say that

Accepted Answer

There will be no net movement across the membrane. Since both solutions have the same molarity (0.1 M), their osmotic pressures are equal, and there will be no net movement of water or solutes across the semi-permeable membrane.

Question 20

Which of the following aqueous solution has minimum freezing point?

Accepted Answer

0.005 m MgI2. Freezing point depression depends on the van 't Hoff factor (i), which accounts for the number of particles in solution. MgI2 dissociates into three ions (Mg²⁺ and 2I⁻), giving it the highest effective concentration of particles, leading to the lowest freezing point.

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