Relative Lowering of Vapour Pressure

Q. If a non-volatile solute (urea) needs to be dissolved in $100g$ of water in order to decrease the vapour pressure of water by $25\%$, then what will be the molality of solution?

1. $18.52m$
2. $16.52m$
3. $19.52m$
4. $15.52m$

Q.

Calculate the mass percentage of benzene (C₆H₆) and carbon tetrachloride (CCl₄) if 22 g of benzene is dissolved in 122 g of carbon tetrachloride.

Q. The vapour pressure of pure benzene at a certain temperature is 0.850 bar. A non-volatile, non-electrolyte solid weighing 0.5 g when added to 39.0 g of benzene (molar mass $78gmo{l}^{-1})$. The vapour pressure of the solution then is 0.845 bar. What is the molar mass of the solid substance?

1. $170gmo{l}^{-1}$
2. $270gmo{l}^{-1}$
3. $370gmo{l}^{-1}$
4. $140gmo{l}^{-1}$

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. 199.34 mm

2. 141.43 mm

3. 143.99 mm

4. 94.39 mm

Q.

QUESTION 2.15

An aqueous solution of $2\%$ non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute?

Q.

Benzene and toluene form ideal solution over the entire range of composition.

The vapour pressure of pure benzene and naphthalene at 300 Kare 50.71

mm Hg and 32.06 mm Hg respectively. Calculate the mole fraction of benzene

in vapour phase if 80 g of benzene is mixed with 100 g of toluene.

Q.

The vapour pressure of dilute aqueous solution of glucose is 750 mm of Hg at 373 K. The mole fraction of glucose is :

1. $\frac{1}{35}$
2. $\frac{1}{76}$
3. $\frac{1}{10}$
   
4. $\frac{1}{7.6}$
   

Q.

QUESTION 2.17

The vapour pressure of water is 12.3 kPa at 300 K. Calculate vapour pressure of 1 molal solution of a non-volatile solute in it.

Q. (a) 30 g of urea (m = 60 g $mo{l}^{-1}$) is dissolved in 846 g of water. Calculate the vapour pressure of water for this solution if vapour pressure of pure water at 298 K is 23.8 mm Hg.
(b) Write two differences betwen ideal solutions and non- ideal solutions.

Q.

QUESTION 2.18

Calculate the mass of a non-volatile solute (molar mass $40gmo{l}^{-1}$) which should be dissolved in 114g octane to reduce its vapour pressure to $80\%$.

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. Ratio of $\frac{\Delta T}{K_b}\text{of}10\text{g}A{B}_2\text{and}14\text{g}{A}_{2}B$ per $100\text{g}$ of solvent in their respective solution ($A{B}_2\text{and}{A}_{2}B$ both are non-electrolytes) is $1$ mol/kg in both cases. Hence, relative atomic mass of $A$ and $B$ are respectively:

1. $60,20$
2. $20,60$
3. $100,40$
4. None of these

Q.

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

1. 0.1(N)BaCl₂

2. 0.1(M)KCl

3. None of these

4. 0.1(M)NaCl

Q. The vapour pressure of a solution of a non-volatile electrolyte (A) in a solvent (B) is 95% of the vapour pressure of the solvent at the same temperature. If $M_B=0.3M_A,$ where $M_A$ and $M_B$ are molecular weights of (A) and (B) respectively, then the weight ratio of the solvent and solute are

1. 69.8
2. 66.6
3. 5.7
4. 76.6

Q. Dry air was passed successively through a solution of 5 g of the solute in 180 g of water and then through pure water. The loss in the weight of solution was 2.50 g and that of pure solvent 0.04 g. The molecular weight of the solute is

1. 31.25
2. 3.125
3. 312.5
4. None

Q. The vapour pressure of pure water is 760 mm at 25^°C . The vapour pressure of solution containing 1(m) solution of glucose will be ??

Q.

What happens to the vapour pressure when a) volatile solute dissolves in the liquid b) the dissolved solute is non volatile

Q.

A solution has 2:3 molar ratio of toluene to benzene. The vapour pressure of benzene and toluene at 25 degree Celsius are 95 and 28 bar respectively. The mole fraction of toulene vapour is?

Q.

QUESTION 2.19

A solution containing 30 g of non-volatile solute exactly in 90 g of water has a vapour pressure of 2.8 kPa at 298 K. Further, 18 g of water is then added to the solution and the new vapour pressure becomes 2.9 k Pa at 298 K. Calculate (i) molar mass of the solute (ii) vapour pressure of water at 298 K.

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. 180
2. 60
3. 342
4. 18

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 100g of acetone at ${20}^{\circ }C$, its vapour pressure was 183 Torr. The molar mass of the substance is

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

Q.

what is gay lussac's law of combining volumes of gases

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. 120

2. 180

3. 380

4. 60

Q.

Suggest a way to determine the value of water.

Q.

If P⁰ and P are the vapour pressure of a solvent and its solution respectively and N₁ and N₂ are the mole fractions of the solvent and solute respectively, then correct relation is

1. 

2. 

3. 

4. 

Q. Which of the following solutions in water will have the lowest vapour pressure

1. 0.1 M, NaCl
2. 
3. 
4. 0.1 M, Sucrose

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.

The mole fraction of benzene in a solution in Toluene is 0.40. Calculate the weight percent of benzene in the solution.

Q. $3g$ urea is dissolved in $45g$ of water. The relative lowering of vapour pressure is :

1. $0.05$
2. $0.01$
3. $0.04$
4. $0.02$

Q.

which of the following solution has maximum value of freezing point

1. H2O

2. 0.1 M NaCl

3. 0.01 NaCl

4. 10.001 M NaCl