Solutions

JEE Chemistry · 84 questions · Page 1 of 9 · Click an option or "Show Solution" to reveal answer

Q1
If liquids A and B form an ideal solution
A the entropy of mixing is zero
B the free energy of mixing is zero
C the free energy as well as the entropy of mixing are each zero
D the enthalpy of mixing is zero
Correct Answer
Option D
Solution

When

AA

and

BB

from an ideal solution,

ΔHmix=0\Delta {H_{mix}} = 0
Q2
K2Hgl4 is 40% ionised in aqueous solution. The value of its van't Hoff factor (i) is:
A 1.6
B 2.2
C 2.0
D 1.8
Correct Answer
Option D
Solution

K2Hgl4 is 40% ionised. \therefore α\alpha =

40100{{40} \over {100}}

= 0.4 K2[Hgl4] \to 2K+ + [Hgl4]2+ N =

2+11{{2 + 1} \over 1}

= 3 i = 1 + (N - 1)α\alpha = 1 + (3 - 1)0.4 = 1 + 2×\times0.4 = 1.8

Q3
In a 0.2 molal aqueous solution of a weak acid HX the degree of ionization is 0.3. Taking kf for water as 1.85, the freezing point of the solution will be nearest to
A -0.360oC
B -0.260oC
C +0.480oC
D -0.480oC
Correct Answer
Option D
Solution
ΔTf=Kf×m×i;\Delta {T_f} = {K_f} \times m \times i;
ΔTf=1.855×0.2×1.3=0.480C\Delta {T_f} = 1.855 \times 0.2 \times 1.3 = {0.480^ \circ }C

\therefore

Tf=00.480C=0.480C\,\,\,{T_f} = 0 - {0.480^ \circ }C = - {0.480^ \circ }C
(HX10.3H+0.3+X0.3,i=1.3)\mathop {\left( {HX} \right.}\limits_{1 - 0.3} \,\,\rightleftharpoons\,\,\mathop {{H^ + }}\limits_{0.3} + \mathop {{X^ - }}\limits_{0.3} ,i = 1.\left. 3 \right)
Q4
Consider a binary solution of two volatile liquid components 1 and 2.x12 . x_1 and y1y_1 are the mole fractions of component 1 in liquid and vapour phase, respectively. The slope and intercept of the linear plot of 1x1\dfrac{1}{x_1} vs 1y1\dfrac{1}{y_1} are given respectively as :
A P10P20,P10P20P20\dfrac{\mathrm{P}_1^0}{\mathrm{P}_2^0}, \dfrac{\mathrm{P}_1^0-\mathrm{P}_2^0}{\mathrm{P}_2^0}
B P20P10,P20P10P20\dfrac{\mathrm{P}_2^0}{\mathrm{P}_1^0}, \dfrac{\mathrm{P}_2^0-\mathrm{P}_1^0}{\mathrm{P}_2^0}
C P20P10,P10P20P20\dfrac{\mathrm{P}_2^0}{\mathrm{P}_1^0}, \dfrac{\mathrm{P}_1^0-\mathrm{P}_2^0}{\mathrm{P}_2^0}
D P10P20,P20P10P20\dfrac{\mathrm{P}_1^0}{\mathrm{P}_2^0}, \dfrac{\mathrm{P}_2^0-\mathrm{P}_1^0}{\mathrm{P}_2^0}
Correct Answer
Option D
Solution

For a binary solution of two volatile liquid components labeled 1 and 2, let x1 x_1 and y1 y_1 represent the mole fractions of component 1 in the liquid and vapor phases, respectively.

The linear relationship between the inverse of these mole fractions is plotted as 1x1\dfrac{1}{x_1} versus 1y1\dfrac{1}{y_1}.

To derive the slope and intercept of this linear plot, consider the following calculations: Using Raoult's Law for a Liquid Solution: For a liquid solution with volatile components 1 and 2: P1=PTy1=P1ox1 \mathrm{P}_1 = \mathrm{P}_{\mathrm{T}} \cdot y_1 = \mathrm{P}_1^{\mathrm{o}} \cdot x_1 Therefore: PTx1=P1oy1 \dfrac{\mathrm{P}_{\mathrm{T}}}{x_1} = \dfrac{\mathrm{P}_1^{\mathrm{o}}}{y_1} Rearranging the Equation: By substituting and rearranging, we have: P2o+x1(P1oP2o)x1=P1oy1 \dfrac{\mathrm{P}_2^{\mathrm{o}} + x_1(\mathrm{P}_1^{\mathrm{o}} - \mathrm{P}_2^{\mathrm{o}})}{x_1} = \dfrac{\mathrm{P}_1^{\mathrm{o}}}{y_1} Simplifying further: P2ox1+(P1oP2o)=P1oy1 \dfrac{\mathrm{P}_2^{\mathrm{o}}}{x_1} + (\mathrm{P}_1^{\mathrm{o}} - \mathrm{P}_2^{\mathrm{o}}) = \dfrac{\mathrm{P}_1^{\mathrm{o}}}{y_1} Expressing 1x1\dfrac{1}{x_1}: Solving for 1x1\dfrac{1}{x_1}, we obtain: 1x1=(P1oP2o)(1y1)+(P2oP1oP2o) \dfrac{1}{x_1} = \left(\dfrac{\mathrm{P}_1^{\mathrm{o}}}{\mathrm{P}_2^{\mathrm{o}}}\right)\left(\dfrac{1}{y_1}\right) + \left(\dfrac{\mathrm{P}_2^{\mathrm{o}} - \mathrm{P}_1^{\mathrm{o}}}{\mathrm{P}_2^{\mathrm{o}}}\right) Determining the Slope and Intercept: The slope of the line is: Slope=P1oP2o \text{Slope} = \dfrac{\mathrm{P}_1^{\mathrm{o}}}{\mathrm{P}_2^{\mathrm{o}}} The intercept of the line is: Intercept=P2oP1oP2o \text{Intercept} = \dfrac{\mathrm{P}_2^{\mathrm{o}} - \mathrm{P}_1^{\mathrm{o}}}{\mathrm{P}_2^{\mathrm{o}}} In summary, for the plot of 1x1\dfrac{1}{x_1} against 1y1\dfrac{1}{y_1}, the slope is P1oP2o\dfrac{\mathrm{P}_1^{\mathrm{o}}}{\mathrm{P}_2^{\mathrm{o}}} and the intercept is P2oP1oP2o\dfrac{\mathrm{P}_2^{\mathrm{o}} - \mathrm{P}_1^{\mathrm{o}}}{\mathrm{P}_2^{\mathrm{o}}}.

Q5
18 g of glucose (C6H12O6) is added to 178.2 g of water. The vapour pressure of water for this aqueous solution at 100oC is
A 759.00 Torr
B 7.60 Torr
C 76.00 Torr
D 752.40 Torr
Correct Answer
Option D
Solution

Moles of glucose

=18180=0.1= {{18} \over {180}} = 0.1

Moles of water

=178.218=9.9= {{178.2} \over {18}} = 9.9

Total moles

=0.1+9.9=10= 0.1 + 9.9 = 10
PH2O={P_{{H_2}O}} =

Mole fraction ×\times Total pressure

=9.910×760= {{9.9} \over {10}} \times 760
=752.4= 752.4\,\,

Torr

Q6
Benzene and toluene form nearly ideal solutions. At 20 oC, the vapour pressure of benzene is 75 torr and that of toluene is 22 torr. The partial vapour pressure of benzene at 20 oC for a solution containing 78 g of benzene and 46 g of toluene in torr is
A 50
B 25
C 53.5
D 37.5
Correct Answer
Option A
Solution

Given, Vapour pressure of benzene

=75torr= 75\,\,torr

Vapour pressure of toluene

=22torr= 22\,\,torr

mass of benzene in

=78g=78g

hence moles of benzene

=7878=1mole= {{78} \over {78}} = 1\,mole

(mol. wt of benzene

=78=78

) mass of toluene in solution

=46g=46g

hence moles of toluene

=4692=0.5mole= {{46} \over {92}} = 0.5\,\,mole

Total moles of benzene and toluene = 1.5 mol now partial pressure of benzene

=Pb×Xb=75×11+0.5= {P^ \circ }_b \times {X_b} = 75 \times {1 \over {1 + 0.5}}
=75×11.5=75×23=50= 75 \times {1 \over {1.5}} = 75 \times {2 \over 3} = 50

torr

Q7
In a mixture of A and B, components show negative deviation when :
A ΔVmix\Delta V_{mix} > 0, ΔSmix\Delta S_{mix} > 0
B ΔVmix\Delta V_{mix} = 0, ΔSmix\Delta S_{mix} > 0
C A - B interaction is weaker than A - A and B - B interaction
D A - B interaction is stronger than A - A and B - B interaction
Correct Answer
Option D
Solution

In the context of solutions and mixtures, a negative deviation from Raoult's law occurs when the interaction between different molecules (A-B interaction) is stronger than the interaction between similar molecules (A-A and B-B interactions).

This is because the molecules prefer to interact with each other rather than themselves, leading to a decrease in the overall vapor pressure compared to what would be expected from Raoult's law.

So, the correct option is : Option D : A - B interaction is stronger than A - A and B - B interaction Option A suggests that the change in volume (ΔVmix\Delta V_{mix}) and change in entropy (ΔSmix\Delta S_{mix}) of the mixture are both greater than zero.

This doesn't necessarily indicate a negative deviation from Raoult's law.

It's possible for these conditions to be true in both positive and negative deviations or even in ideal solutions.

Therefore, this option isn't specifically associated with negative deviations.

Option B suggests that there's no change in the volume of the mixture (ΔVmix=0\Delta V_{mix} = 0) and the change in entropy (ΔSmix\Delta S_{mix}) is greater than zero.

Again, this doesn't specifically indicate a negative deviation from Raoult's law.

The volume change upon mixing can be zero, positive, or negative depending on the nature of the interactions among the molecules.

Raoult's law deviations are primarily dictated by the relative strength of the intermolecular forces among the different components in the mixture.

Thus, the change in volume and entropy, while they can be related, do not directly determine whether a solution will show a positive or negative deviation.

Q8
A pressure cooker reduces cooking time for food because
A boiling point of water involved in cooking is increased
B the higher pressure inside the cooker crushes the food material
C cooking involves chemical changes helped by a rise in temperature
D heat is more evenly distributed in the cooking space
Correct Answer
Option A
Solution

NOTE : On increasing pressure, the temperature is also increased.

Thus in pressure cooker due to increase in pressure the

b.p.b.p.

of water increases.

Q9
Which one of the following statements is false?
A Raoult’s law states that the vapour pressure of a components over a solution is proportional to its mole fraction
B Two sucrose solutions of same molality prepared in different solvents will have the same freezing point depression
C The correct order of osmotic pressure for 0.01 M aqueous solution of each compound is BaCl2 > KCl > CH3COOH > sucrose
D The osmotic pressure (π\pi) = MRT, where M is the molarity of the solution
Correct Answer
Option B
Solution
ΔTf=Kf×m×i.\Delta {T_f} = {K_f} \times m \times i.

Since

Kf{K_f}

has different values for different solvents, hence even if the

mm

is the same

ΔTf\Delta {T_f}

will be different

Q10
A binary liquid solution is prepared by mixing n-heptane and ethanol. Which one of the following statements is correct regarding the behaviour of the solution ?
A The solution formed is an ideal solution
B The solution is non-ideal, showing +ve deviation from Raoult’s law.
C The solution is non-ideal, showing –ve deviation from Raoult’s law.
D n-heptane shows +ve deviation while ethanol shows –ve deviation from Raoult’s law.
Correct Answer
Option B
Solution

For this solution intermolecular interactions between

nn

-heptane and ethanol aare weaker than

nn

-heptane -

nn

- heptane & ethanol-ethanol interactions hence the solution of

nn

-heptane and ethanol is non-ideal and shows positive deviation from Raoult's law.

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