1
MCQ (Single Correct Answer)

NEET 2016 Phase 1

Which of the following statements about the composition of the vapour over an ideal 1 : 1 molar mixture of benzene and toluene is correct? Assume that the temperature is constant at 25oC. (Given, vapour pressure data at 25oC, benzene = 12.8 kPa, toluene = 3.85 kPa)
A
The vapour eill contain equal amounts of benzene and toluene.
B
Not enough information is given to make a prediction.
C
The vapour will contain a higher percentage of benzene.
D
The vapour will contain a higher percentage of toluene

Explanation

pBenzene = xBenzene. poBenzene

pToluene = xToluene. poToluene

For an ideal 1 : 1 molar mixture of benzene and toluene

xBenzene = $${1 \over 2}$$ and xToluene = $${1 \over 2}$$

pBenzene = $${1 \over 2}$$poBenzene = $${1 \over 2} \times 12.8$$ = 6.4 kPa

pToluene = $${1 \over 2}$$poToluene = $${1 \over 2} \times 3.85$$ = 1.925 kPa

Thus, the vapour will contain a high percentage of benzene as the partial vapour pressure of benzene is higher as compared to that of toluene.
2
MCQ (Single Correct Answer)

NEET 2016 Phase 2

Which one of the following is incorrect for ideal solution?
A
$$\Delta {H_{mix}} = 0$$
B
$$\Delta {U_{mix}} = 0$$
C
$$\Delta P = {P_{obs}} - P$$calculated by Raoult's law
D
$$\Delta {G_{mix}} = 0$$

Explanation

For ideal solution, we have

$$\Delta $$Hmix = 0, $$\Delta $$Vmix = 0

Now Umix = ∆Hmix – P$$\Delta $$Vmix

$$ \therefore $$ $$\Delta $$Umix = 0

Also, for an ideal solution,

pA = xApAo, pB = xBpBo

$$ \therefore $$ $$\Delta $$p = pobserved – pcalculated = 0

$$\Delta $$Gmix = $$\Delta $$Hmix – T$$\Delta $$Smix

For an ideal solution, $$\Delta $$Smix $$ \ne $$ 0

$$ \therefore $$ $$\Delta $$Gmix $$ \ne $$ 0
3
MCQ (Single Correct Answer)

NEET 2016 Phase 2

The van't Hoff factor (i) for a dilute aqueous solution of the strong electrolyte barium hydroxide is
A
0
B
1
C
2
D
3

Explanation

Ba(OH)2 is a strong electrolyte and undergoes cent percent dissociation in a dilute aqueous solution.

Ba(OH)2(aq) $$ \to $$ Ba2+(aq) + 2OH(aq)

Thus, van’t Hoff factor i = 3.
4
MCQ (Single Correct Answer)

AIPMT 2015 Cancelled Paper

Which one of the following electrolytes has the same value of van't Hoff factor (i) as that of Al2(SO4)3 (if all are 100% ionised)?
A
Al(NO3)3
B
K4[Fe(CN)6]
C
K2SO4
D
K3[Fe(CN)6]

Explanation

Ai2(SO4)3 ⇌ 2Al+3 + 3SO42–

van't Hoff factor, i = 5

K2SO4 ⇌ 2K+ + SO42–

van't Hoff factor, i = 3

K3[Fe(CN)6] ⇌ 3K+ + [Fe(CN)6]2-

van't Hoff factor, i = 4

Al(NO3)3 ⇌ Al3+ + 3NO3

van't Hoff factor, i = 4

K4[Fe(CN)6] ⇌ 4K+ + [Fe(CN)6]4–

van't Hoff factor, i = 5

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