Relative Lowering of Vapour Pressure

Q. $6.0g$ of urea $(\text{Molar mass}=60g/mol)$ was dissolved in $9.9mol$ of water. If the vapour pressure of pure water is $P_A^{\circ },$ the vapour pressure of solution is:

1. $0.10P_A^{\circ }$
2. $1.01P_A^{\circ }$
3. $0.90P_A^{\circ }$
4. $0.99P_A^{\circ }$

Q. Mass of non-volatile solute (urea) needs to be dissolved in 100 g of water in order to decrease the vapour pressure of water by 30%. What will be the molality of solution?

1. 23.88 m
2. 28.88 m
3. 25.88 m
4. 35.88 m

Q.

What does Raoults law state?

Q.

At 300K, when a solute is added to a solvent its vapour pressure over mercury reduces from 50 mm to 45 mm. The value of mole fraction of solute will be:

1. 0.005
2. 0.010
3. 0.100
4. 0.900

Q. 18 g of glucose $\left(C_6{H}_{12}{O}_6\right)$ is added to 178.2 g of water. The vapour pressure of water for this aqueous solution at ${100}^{\circ }C$ is

1. 759.00 torr
2. 7.60 torr
3. 76.00 torr
4. 752.40 torr.

Q.

Vapour pressure of CCl₄ at 25⁰C is 143mm of Hg. 0.5 gm of a non-volatile solute (mol. wt. = 65) is dissolved in 100ml CCl₄. Find the vapour pressure of the solution (Density of CCl₄=1.58g/cm²)

1. 141.43 mm

2. 94.39 mm

3. 199.34 mm

4. 143.99 mm

Q.

Which of the following solution in water possesses the lowest vapour pressure:

1. 0.1 M NaCl

2. 0.1 N BaCl₂

3. 0.1 M KCl

4. None of these

Q. Which of the following is a property of ammonia?

Q. The vapour pressure of a solution of a non-volatile electrolyte $\text{a}$. in a solvent $\text{b}$. is 95% of the vapour pressure of the solvent at the same temperature. If $M_B=0.3M_A$, where $M_B$ and $M_A$ are molar masses of $B$ and $A$ respectively, the mass ratio of the solvent and the solute are:

1. 0.015
2. 5.7
3. 0.2
4. 4

Q.

The vapour pressure of pure benzene $C_6{H}_6$ at ${50}^{\circ }C$ is 268 torr. How many moles on non-volatile solute per mole of benzene is required to prepare a solution of benzene having a vapour pressure of 167 torr at ${50}^{\circ }C$?

1. 0.377

2. 0.605

3. 0.623

4. 0.395
   

Q. A saturated solution of $XC{l}_3$ has a vapour pressure of 17.20 mm Hg at 20$°C$, while pure water vapour pressure is 17.25 mm Hg. Solubility product ($K_{sp}$) of $XC{l}_3$ at 20$°C$ is:

1. $9.80\times {10}^{-2}$
2. $9.45\times {10}^{-6}$
3. $2.56\times {10}^{-6}$
4. $6.91\times {10}^{-5}$

Q. 5 cm³ of acetone is added to 100cm³ of water, the vapour pressure of water over the solution

1. It will be equal to the vapour pressure of pure water
2. It will be less than the vapour pressure of pure water
3. It will be greater than the vapour pressure of pure water
4. It will be very large

Q.

A solution has a 1 : 4 mole ratio of pentane to hexane. The vapour pressure of the pure hydrocarbons at 20°Care 440mmHg for pentane and 120mm Hg for hexane. The mole fraction of pentane in the vapour phase would be:

1. 0.549

2. 0.200

3. 0.786

4. 0.478

Q.

The relative lowering of vapour pressure produced by dissolving 71.5 g of a substance in 1000 g of water is 0.00713. The molecular weight of the substance will be:

1. 18.0

2. 342

3. 60

4. 180

Q.

The vapour pressure of acetone at ${20}^{\circ }C$ is 185 torr. When 1.2 g of a non-volatile substance was dissolved in 100 g of acetone at ${20}^{\circ }C$, its vapour pressure was 183 torr. The molar mass $\left(gmo{l}^{-1}\right)$ of the substance is:

1. 32

2. 64

3. 128

4. 488

Q.

Vapour pressure of a solution of 5g of non-electrolyte in 100g of water at a particular temperature is 2985 N/m². The vapour pressure of pure water is 3000 N/m². The molecular weight of the solute is:

1. 60

2. 120

3. 180

4. 380

Q. Certain mass of a non-volatile solute (urea) when dissolved in $100\text{g}$ of water decreased the vapour pressure of water by $30\%$. What is the molality of the solute in the solution?

1. 30.52 m
2. 28.20 m
3. 23.81 m
4. 35.62 m

Q. The vapour pressure of acetone at ${20}^{\circ }$$C$ is 185 $torr$. When 1.2 $g$ of a non-volatile substance was dissolved in 100 $g$ of acetone at ${20}^{\circ }$$C$, its vapour pressure was 183 $torr$. The molar mass $\left(g/mol\right)$ of the substance is:

1. 32
2. 64
3. 128
4. 488

Q. Calculate the weight of non-volatile solute (in grams) having molecular weight $40\text{u}$, which should be dissolved in $57\text{g}$ octane to reduce its vapour pressure to $80\%$: