CBSE Questions for Class 12 Engineering Chemistry Solutions Quiz 5 - MCQExams.com

At $$25^oC$$, the total pressure of an ideal solution obtained by mixing 3 mole of A and 2 mole of B, is 184 torr. What is the vapour pressure (in torr) of pure B at the same temperature (Vapour pressure of pure A at $$25^oC$$ is 200 torr.)?
  • 180
  • 160
  • 16
  • 100
An aqueous solution containing $$28\%$$ by mass of a liquid A (molecular mass = 140) has a vapour pressure of 160 mm at $$37^oC$$. Find the vapour pressure of pure liquid A (the vapour pressure of water $$37^oC$$ is 150 mm).
  • $$p_A=358.3 mm$$
  • $$p_A=388.3 mm$$
  • $$p_A=258.3 mm$$
  • None of these
Among the following, that does not form an ideal solution is:
  • $$C_6H_6$$ and $$C_6H_5CH_3$$
  • $$C_2H_5Cl$$ and $$C_2H_5OH$$
  • $$C_6H_5Cl$$ and $$C_6H_5Br$$
  • $$C_2H_5Br$$ and $$C_2H_5I$$
The depressions in freezing point for 1 m urea, 1 m glucose and 1 m NaCl are in the ratio:
  • 1 : 2 : 3
  • 3 : 2 : 2
  • 1 : 1 : 2
  • None of these
Which one of the following is a primary standard?
  • Oxalic acid
  • Sodium thiosulphate
  • Sodium hydroxide
  • Potassium dichromate
18 g glucose is dissolved in 90 g of water. The relative lowering of vapour pressure of the solution is equal to__________.
  • 6
  • 0.2
  • 5.1
  • 0.02
X is a non-volatile solute and Y is volatile solvent. The following vapour pressures are obtained by dissolving X in Y.
X/mol $$L^{-1}$$Y/mm Hg
0.1$$P_1$$
0.25$$P_2$$
0.01$$P_3$$
The correct order of vapour pressure is :
  • $$P_1 < P_2 < P_3$$
  • $$P_3 < P_2 < P_1$$
  • $$P_3 < P_1 < P_2$$
  • $$P_2 < P_1 < P_3$$
The freezing point depression constant for water is $$1.86^oC$$ $$m^{-1}$$. If $$5$$ g $$Na_2SO_4$$ is dissolved in 45 g $$H_2O$$, the freezing point is changed by  $$-3.82^oC$$. 
Calculate the van't Hoff factor for $$Na_2SO_4$$.
  • $$0.381$$
  • $$2.05$$
  • $$2.63$$
  • $$3.11$$
An aqueous solution is $$1$$ molal in $$KI$$. Which change will cause the vapour pressure of the solution to increase?
  • Addition of $$NaCl$$
  • Addition of $$Na_2SO_4$$
  • Addition of $$1$$ molal $$KI$$
  • Addition of water
If the various terms in the following expressions have usual meanings, the van't Hoff factor 'i' cannot be calculated by which of the following expression?
  • $$\pi V=\sqrt{i}nRT$$
  • $$\triangle T_f=i\times K_f\times m$$
  • $$\triangle T_b=i\times K_b\times m$$
  • $$\dfrac{p^o_{solvent}-p_{solution}}{p^o_{solvent}}=i\begin{bmatrix}\dfrac{n}{N+n}\end{bmatrix}$$
Which of the following property indicates weak intermolecular forces of attraction in liquid?
  • High heat of vaporization
  • High vapour pressure
  • High critical temperature
  • High boiling point
Choose the correct statement, when the concentration of a salt solution is increased:
  • Boiling point increases while vapour pressure decreases
  • Boiling point decreases while vapour pressure increases
  • Freezing point decreases while vapour pressure increases
  • Freezing point increases while vapour pressure decreases
Two liquids $$A$$ and $$B$$ form an ideal solution. At $$300K,$$ the VP of solution containing one mole of $$ 'A'$$ and $$4$$ mole $$'B'$$ is $$560 mm $$ $$Hg. $$ At the same temp, if one mole of $$'B'$$ is taken out from the solution the VP of the solution has decreased by $$10mm$$ $$Hg,$$ the VP of pure $$A\ \& \ B$$ are (in mm):
  • $$ 400, 600$$
  • $$500,500$$
  • $$300, 700$$
  • $$200,800$$
If in a solvent, n simple molecules of solute combine to form an associated molecule, $$\alpha$$ is the degree of association, the van't Hoff's factor is equal to :
  • $$\cfrac {1}{1-n\alpha }$$
  • $$1 -\alpha +n\alpha $$
  • $$1-\alpha +\cfrac {\alpha}{n}$$
  • $$\cfrac {\alpha}{n} -1 +\alpha$$
Van't Hoff factor, when benzoic acid is dissolved in benzene, will be:
  • $$2$$
  • $$1$$
  • $$0.5$$
  • $$1.5$$
The vapour pressure of a solvent decreased by $$10\ mm$$ of mercury when a non-volatile solute was added to the solvent. The mole fraction of the solute in the solution is $$0.2$$. What should be the mole fraction of the solvent, if the decrease in the vapour pressure is to be $$20\ mm$$ of mercury?
  • $$0.8$$
  • $$0.6$$
  • $$0.4$$
  • $$0.2$$
At a constant temperature, which of the following aqueous solutions will have the maximum vapour pressure?

[Mol weight: $$NaCl=58.5,{ H }_{ 2 }{ SO }_{ 4 }=98.0g.{ mol }^{ -1 }$$]
  • $$1$$ molal $$NaCl$$
  • $$1$$ molar $$NaCl$$
  • $$1$$ molal $${H}_{2}{SO}_{4}$$
  • $$1$$ molar $${H}_{2}{SO}_{4}$$
Two liquids $$A$$ and $$B$$ form an ideal solution. What is the vapour pressure of solution containing $$2$$ moles of $$A$$ and $$3$$ moles of $$B$$ at $$300\ K$$? 
[Given: At $$300\ K$$, vapour pressure of pure liquid $$A(P_{A}^{\circ}) = 100\ torr$$, Vapour pressure of pure liquid $$B(P_{B}^{\circ}) = 300\ torr]$$.
  • $$200\ torr$$
  • $$220\ torr$$
  • $$180\ torr$$
  • None of these
A cylinder filled with a movable piston contains liquid water in equilibrium with water vapour at $${ 25 }^{ o }C$$. Which one of the following operations results in a decrease in the equilibrium vapour pressure?
  • Moving piston downward a short distance
  • Removing a small amount of vapour
  • Removing a small amount of the liquid water
  • Dissolving salt in the water
On the surface of the earth at $$1\ atm$$ pressure, a balloon filled with $$H_{2}$$ gas occupies $$500\ mL$$. This volume is $$5/6$$ of its maximum capacity. The balloon is left in air. It starts rising. The height above which the balloon will burst if temperature of the atmosphere remains constant and the pressure decreases $$1\ mm$$ for every $$100\ cm$$ rise of height is:
  • $$120\ m$$
  • $$136.67\ m$$
  • $$126\ m$$
  • $$100\ m$$
Lowering of vapour pressure in $$2$$ molal aqueous solution at $$373K$$ is____________.
  • $$0.35$$ bar
  • $$0.022$$ bar
  • $$0.22$$ bar
  • $$0.035$$ bar
The vapour pressure of pure liquid $$A$$ at $$300\ K$$ is $$577\ Torr$$ and that of pure liquid $$B$$ is $$390\ Torr$$. These two compounds form ideal liquid and gaseous mixtures. Consider the equilibrium composition of a mixture in which the mole fraction of $$A$$ in the vapour is $$0.35$$. Find the mole % of $$A$$ in liquid.
  • 0.628
  • 0.872
  • 0.267
  • 0.834
The freezing point depression constant for water is $$-1.86C$$. If $$5.00$$ g of $${ Na }_{ 2 }{ SO }_{ 4 }$$ is dissolved in $$45.0$$ g $${ H }_{ 2 }O$$. The freezing point is changed by $$-3.82C$$. 
Calculate the van't Hoff factor?
  • $$2.63$$
  • $$0.311$$
  • $$0.38$$
  • $$3.8$$
For the reversible reaction.
$$N_2 (g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$$
at $$500^o$$ C, the value of $$K_p$$ is $$1.44 \times 10^{-5} \ atm^{-2}$$ when partial pressure is measured in atmosphere. The corresponding value of $$K_c$$, with concentration in $$mol/ L$$ is:
  • $$\displaystyle \frac{1.44 \times 10^{-5}}{(0.082 \times 500)^{-2}}$$
  • $$\displaystyle \frac{1.44 \times 10^{-5}}{(8.314 \times 773)^{-2}}$$
  • $$\displaystyle \frac{1.44 \times 10^{-5}}{(0.082 \times 773)^{2}}$$
  • $$\displaystyle \frac{1.44 \times 10^{-5}}{(0.082 \times 773)^{-2}}$$
If relative decrease in vapour pressure is $$0.4$$ for a solution containing $$1$$ mol $$NaCl$$ in $$3$$ mol $$H_{2}O$$. 
$$NaCl$$ is_____ % ionized.
  • $$60$$%
  • $$50$$%
  • $$100$$%
  • $$40$$%
Calculate solubility of $$Pb{I}_{2}$$ ($${K}_{sp}=1/4\times {10}^{-8}$$) in water at $${25}^{o}$$, which is $$90$$% dissociated.
  • $$7.5 \times 10^{-4} \ M$$
  • $$1.6 \times 10^{-3} \ M$$
  • $$3.4 \times 10^{-3} \ M$$
  • $$8.2 \times 10^{-3} \ M$$
Water and chlorobenzene are immiscible liquids. Their mixture boils at $$89^o$$C under a reduced pressure of $$7.7 \times 10^4$$ Pa. The vapour pressure of pure water at $$89^o$$C is $$7 \times 10^4$$ Pa. Weight percent of chlorobenzene in the distillate is:
  • 50
  • 60
  • 79
  • 38.46
The $$K_{sp}$$ for $$Cr(OH)_3$$ is $$1.6 \times 10^{-30}$$. The solubility of this compound in water is:
  • $$4 \sqrt{1.6\times10^{-30}}$$
  • $$4 \sqrt{1.6\times10^{-30} / 27}$$
  • $$1.6\times10^{-9}$$
  • $$2 \sqrt{1.6\times10^{-30}}$$
The vapour pressure of the solution of two liquids $$A({p}^{o}=80mm$$) and $$B({p}^{o}=120mm)$$ is found to be $$100mm$$ when $${x}_{A}=0.4$$. The result shows that:
  • solution exhibits ideal behaviour
  • solution shows positive deviations
  • solution shows negative deviations
  • solution will show positive deviations for lower concentration and negative deviations for higher concentrations
$$A$$ and $$B$$ form ideal solutions, at $${50}^{o}C$$, $${P}_{A}^{o}$$ is half $${P}_{B}^{o}$$. A solution containing $$0.2$$ mole of $$A$$ and $$0.8$$ mole of $$B$$ has a normal boiling point of $${50}^{o}C$$. Find $$18\times {P}_{B}^{o}$$. ($${P}_{B}^{o}$$ is in atm)
  • 0.24
  • 0.34
  • 0.53
  • 0.46
The ratio of the vapour pressure of a solution to the vapour pressure of the solvent is:
  • equal to the mole fraction of the solvent
  • equal to the mole fraction of the solute
  • directly proportional to mole fraction of the solute
  • None of the above
Vapour Pressure of a mixture of benzene and toluene is given by $$P= 179X_{B} + 92$$, Where $$X_{B}$$ is mole fraction of benzene.
If Vapours are removed and condensed in to liquid then what will be the ratio of mole fraction of benzene and toluene in first condensate :
  • 2.8
  • 1.5
  • 3.5
  • 4.5
What is the solubility of $$Al(OH_{3}), K_{sp} = 1 \times 10^{-33}$$, in a solution having $$pH = 4$$?
  • $$6 \times 10^{-3}$$M
  • $$10^{-6}$$M
  • $$1.5 \times 10^{-4}$$M
  • $$2.47 \times 10^{-9}$$M
At a given temperature, total vapour pressure in Torr of a mixture volatile components A and B is given by 
$$P_{Total}=120-75X_B$$
Hence, vapour pressure of pure A and B respectively (in Torr) are ?
  • 120, 75
  • 120, 195
  • 120, 45
  • 75, 45
Vapour Pressure of a mixture of benzene and toluene is given by $$P= 179X_{B} + 92$$, Where $$X_{B}$$ is mole fraction of benzene.
Vapour pressure of the solution obtained by mixing 936 g of benzene and 736 gm of toluene :
  • 199.4 mm
  • 271 mm
  • 280 mm
  • 289 mm
At $$80^0$$C, the vapour pressure of pure liquid A is $$250$$mm of Hg and that of pure liquid B is $$1000$$ mm of Hg. If a solution of A and B boils at $$80^0$$C and $$1$$ atm pressure, the amount of A in the mixture is :$$(1atm = 760mm$$Hg)
  • $$50$$ mole percent
  • $$52$$ mole percent
  • $$32$$ mole percent
  • $$48$$ mole percent
The van't Hoff factor of the benzoic acid solution in benzene is 0.In this solution, benzoic acid:
  • dissociates
  • forms dimer
  • remains unchanged
  • forms tetramer
The vapour pressure of the solution of two liquids $$A(P^{\circ} = 80\ mm)$$ and $$B(p^{\circ} = 120\ mm)$$ is found to be $$100\ mm$$ when $$x_{A} = 0.4$$. The result shows that :
  • Solution exhibits ideal behaviour
  • Solution shows positive deviations
  • Solution shows negative deviations
  • Solution will show positive deviations for lower concentration and negative deviations for higher concentrations
At $$80^o$$C, the vapour pressure of pure liquid $$A$$ is $$250$$ mm of $$Hg$$ and that of pure liquid $$B$$ is $$1000$$ mm of $$Hg$$. If a solution of $$A$$ and $$B$$ boils at $$80^o$$ and $$1$$ atm pressure, the amount of $$A$$ in the mixture is? 
($$1$$ atm $$=760$$ mm Hg).
  • $$50$$ mole percent
  • $$52$$ mole percent
  • $$32$$ mole percent
  • $$48$$ mole percent
At 80C, the vapour pressure of pure benzene is 753 mm Hg and of pure toluene 290 mm Hg. Calculate the composition of a liquid in mole percent which at $$80$$ is in equilibrium with vapour containing 30 mole percent of benzene. 
  • 24, 56
  • 26 ,54
  • 56 24
  • 34 ,76
Two moles of pure liquid 'A' ($$P^o_A$$ = 80mm of Hg) and 3 moles of pure liquid 'B' ($$P^o_B$$ = $$120$$mm of $$Hg$$) are mixed. Assuming ideal behaviour.
  • Vapour pressure of the mixture is $$104$$ mm of $$Hg$$
  • Mole fraction of liquid '$$A'$$ in Vapour pressure is $$0.3077$$
  • Mole fraction of '$$B$$' in vapour pressure is $$0.692$$
  • Mole fraction of '$$B$$' in vapour pressure is $$0.785$$
Match the column I with column II and mark the appropriate choice
Column IColumn II
(A) Ethyl alcohol + water(i) $$p={p}^{o}x$$
(B) Benzene + Toulene(ii) Effect of pressure on gas solutions
(C) Henry's law(iii) Ideal solution
(D) Raoult's law(iv) Azeotropic mixture
  • (A) $$\rightarrow$$ (i); (B) $$\rightarrow$$ (ii); (C)$$\rightarrow$$ (iii); (D) $$\rightarrow$$ (iv)
  • (A) $$\rightarrow$$ (i); (B) $$\rightarrow$$ (iii); (C)$$\rightarrow$$ (ii); (D) $$\rightarrow$$ (iv)
  • (A) $$\rightarrow$$ (iv); (B) $$\rightarrow$$ (iii); (C)$$\rightarrow$$ (ii); (D) $$\rightarrow$$ (i)
  • (A) $$\rightarrow$$ (iii); (B) $$\rightarrow$$ (i); (C)$$\rightarrow$$ (i); (D) $$\rightarrow$$ (iv)
What are the conditions for an ideal solution which obeys Raoult's law over the entire range of concentration?
  • $${ \Delta }_{ mix }H=0,{ \Delta }_{ mix }V=0,{ P }_{ Total }={ p }_{ A }^{ o }{ x }_{ A }+{ p }_{ B }^{ o }{ x }_{ B }$$
  • $${ \Delta }_{ mix }H=+ve,{ \Delta }_{ mix }V=0,{ P }_{ Total }={ p }_{ A }^{ o }{ x }_{ A }+{ p }_{ B }^{ o }{ x }_{ B }$$
  • $${ \Delta }_{ mix }H=0,{ \Delta }_{ mix }V=+ve,{ P }_{ Total }={ p }_{ A }^{ o }{ x }_{ A }+{ p }_{ B }^{ o }{ x }_{ B }$$
  • $${ \Delta }_{ mix }H=0,{ \Delta }_{ mix }V=0,{ P }_{ Total }={ p }_{ B }^{ o }{ x }_{ B }$$
For which of the following solutes the van't Hoff factor is not greater than one?
  • $$Na{NO}_{3}$$
  • $$Ba{Cl}_{2}$$
  • $${ K }_{ 4 }\left[ Fe{ \left( CN \right) }_{ 6 } \right] $$
  • $${NH}_{2}CO{NH}_{2}$$
A solute $$X$$ when dissolved in a solvent associate to form a pentamer. The value of van't Hoff factor ($$i$$) for the solute will be:
  • $$0.5$$
  • $$5$$
  • $$0.2$$
  • $$0.1$$
What will be the correct order of vapour pressure of water, acetone and ether at $$30^0$$C. Given that among these compounds, water has maximum boiling point and ether has minimum boiling point.
  • Water < Ether < Acetone
  • Water < Acetone < Ether
  • Ether < Acetone < Water
  • Acetone < Ether < Water
If $$\alpha$$ is the degree of dissociation of $${Na}_{2}{SO}_{4}$$, the vant Hoff's factor ($$i$$) used for calculating the molecular mass is:
  • $$1+\alpha$$
  • $$1-\alpha$$
  • $$1+2\alpha$$
  • $$1-2\alpha$$
$$6 g$$. of the area of dissolved in $$90 g$$. of boiling water. The vapour pressure of the solution is: 
  • $$744.8$$ mm
  • $$758$$ mm
  • $$761$$ mm
  • $$760$$ mm
Among the following substances, the lowest vapour pressure is exerted by:
  • water
  • alcohol
  • ether
  • mercury
The van't Hoff factor of $$0.005M$$ aqueous solution of $$KCl$$ is $$1.95$$. The degree of ionisation of $$KCl$$ is:
  • $$0.95$$
  • $$0.97$$
  • $$0.94$$
  • $$0.96$$
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