Solutions Test 10

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Solutions Test 10

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Question 1
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Only One Option Correct Type
This section contains 13 multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONLY ONE is correct
Elevation in boiling point of an aqueous solution of a non-electrolyte solute is 1.04°. What is the depression in freezing point of this solution?
K_f (H₂0) = 0.52° mol^-1 kg
K_f (H₂0) = 1.86° mol^-1 kg

A
1.86°

B
0.52°

C
3.72°

D
0.93°

Solution
Question 2
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12.8 g of naphthalene (C₁₀H₈) is dissolved in 92 g toluene (C₇H₈). Boiling point of this solution is
(boiling point of toluene = 110°Cand mole fraction boiling point elevation constant of toluene is 36.1 K)

A
149.2°C

B
113.3°C

C
116.7° C

D
111.1° C

Solution

When (K_z) mole fraction boiling point elevation constant is given, then
Thus,boiling point of solution =110+ 3.28 =113.28°C
Question 3
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Elevation in boiling point of a molar (1 M) glucose solution (d = 1.2 g mL^-1) is

A
0.98 K_b

B
K_b

C
1.20K_b

D
1.02 K_b

Solution

(a) Molarity =1 M =1 mol L^-1
1000 mL of solution has glucose = 180 g
(1000 x 1.2) g of solution has glucose = 180g
∴ Solute (w₁) =180 g
Solution =1200 g
Question 4
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For a dilute solution containing 2.5 g of a non-volatile non-electrolyte solute in 100 g water, the elevation in boiling point at 1 atm pressure is 2°C. Assuming concentration of solute is much lower than the concentration of solvent, the vapour pressure (mm of Hg) of the solution is (Take, K_b = 0.76 K mol^-1 kg).
[IITJEE2012]

A
724

B
740

C
736

D
718

Solution
Question 5
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Relative lowering of vapour pressure of a non-volatile solute X in water is 0.05. If K_b(H₂0) = 0.52° mol^-1 kg^-1.
(ΔT_b) = elevation in boiling point assuming a dilute solution
(AT_b)' = elevation in boiling point assuming a solution of moderate concentration then, {ΔT_b) - {ΔT_b)' =

A
zero

B
0.80°

C
-0.08°

D
0.16°

Solution

By Raoult’s law,
If solution is dilute,
If solution is of moderate concentration,
Question 6
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6% aqueous solution of urea (by mass of solvent) has elevation in boiling point xt. 18% aqueous solution of glucose (by mass of solvent) has elevation in boiling point x₂. If these two solutions are mixed then, elevation in boiling point is x₃. Then,

A
x₁ + x₂ = x₃

B
3x₁ + x₂ = x₃

C
x₁ = x₂ = x₃

D
x₁< x₂ < x₃

Solution

Thus, x₁ =x₂ = x₃
Question 7
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AB is a sparingly soluble salt in aqueous solution with K_sp =1x10^-8. If K_b(H₂0 ) = 0.52° mol^-1 kg then elevation in boiling point of saturated solution is

A
5.2 x 10^-5K

B
5.2 x 10^-9K

C
5.2 x 10^-8K

D
5.2 x 10^-4K

Solution

(a) Salt is sparingly soluble hence, can be considered as non-electrolyte.
Since, solubility is very low, molarity can be taken as molality.
Question 8
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Elevation in boiling point of a solution of non-electrolyte in non-polar solvent (toluene) is 0.3°. Mole fraction elevation constant of non-polar solvent is 36.1 K. Thus, molality (mol kg^-1) of the solution is

A
8.31 x 10^-3

B
0.091

C
10.98

D
1.27

Solution

(b) In terms of mole fraction elevation constant
Thus, solute = 0.3 mole
Question 9
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Which of the given aqueous solution has maximum boiling point?
(K_b of H₂0 = 0 .5 2 ° mol^-1kg), T_b (H₂0 ) = 373 K)

A
18% glucose solution by weight of solution

B
34.2% sucrose solution by weight of solution

C
6% urea solution by weight of solution

D
All have equal boiling points

Solution
Question 10
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X and Y both are soluble in given solvent. Molar mass of the polymer Y is

A
50 g mol^-1

B
250 g mol^-1

C
110 g mol^-1

D
200 g mol^-1

Solution
Question 11
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Given, H₂0 ( / ) H₂0 ( g ) a t 373 K, ΔH° = 9.72 kcal mol^-1 and the concentration of the sucrose in water is 0.1 M. Find the elevated boiling point of water.

A
373.52 K

B
373.052 K

C
374.04 K

D
374.52 K

Solution

(b) H₂0 (/) changes to steam FlaO (g) at 373 K. Thus, this represents latent heat of vaporisation. K_b (molal elevation constant) is related to ΔH° and boiling point by equation,
Here, ΔH° is in energy unit per gram of solvent.
ΔT_b (sucrose solution) = molality x K_b - 0.1 x 0.52 = 0.052°
∴Boiling point of solution = 373 + 0.052° = 373.052 K
Question 12
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Glucose solution is 20% by weight of solution. Its boiling point is ........
Given 1 molal urea solution boils at 100.52° C and water boils at 1 atm pressure,

A
100.52°C

B
102.17°C

C
97.83°C

D
100.72°C

Solution

(d)
Water boils at 1 atmospheric pressure. Thus, boiling point of H₂0 =100°C
1 molal urea solution boils at 100.52°C
Glucose solution is 20% by weight of solution.
∴Boiling point of glucose solution = 100.72⁰C
Question 13
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Latent heat of fusion and latent heat of vaporisation of a solvent are in the ratio of 1: 6 and freezing point and boiling point (in Kelvin scale) are in the ratio of 2:3. Thus, ratio of elevation in boiling point to depression in freezing point of 1 molal solution is

A
1/2

B
1/4

C
3/4

D
3/8

Solution

(d) K_b (molal elevation constant) is related to latent heat of vaporisation (ΔH_V)and boiling point (T_b)of solvent by relation.
Similarly, K_f(molal depression constant) is related to latent heat of fusion ((ΔH_f) and boiling point 7, of solvent by relation.