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Multiple Choice Questions

541.

In countries nearer to polar region, the roads are sprinkled with CaCl₂ .This is :

to minimise the wear and tear of the roads
to minimise the snow fall
to minimise pollution
to minimise the accumulation of dust on the road

542.

The solubility of a gas in water at 300 K under a pressure of 100 atm is 4 x 10^-3 kg L^-1. Therefore, the mass of the gas in kg dissolved 250 mL of water under a pressure of 250 atm at 300 K is :

2.5 x 10^-3
2.0 x 10^-3
1.25 x 10^-3
5.0 x 10^-3

543.
The depression in freezing point of 0.1 M aqueous solutions of HCl, CuSO₄ and K₂SO₄ are in the ratio

1 : 1 : 1.5

1 : 2 : 3

1 : 1 : 1

2 : 4 : 3

1 : 1 : 1.5

The depression in freezing point is calculated by the expression:

$∆$ T_f = iK_fm

(where, $∆$ T = depression in freezing point; i = vant hoff factor; K = constant; M = molarity of the solution)

Thus, $∆$ T_f $\propto$ i (as concentration is same for all solutions)

Let us consider that all compounds dissociate 100% (as i depends on the no. of total no. of ions that the molecules will produce on being dissociated ).

HCl will give 2 ions H⁺ and Cl^-. Hence, its vant hoff factor is 2.

CuSO₄ will give 2 ions Cu²⁺ and SO $_{4}^{2 -}$ . Hence, its vant hoff factor is 2.

K₂SO₄ will give 3 ions, two K⁺ ions and one SO $_{4}^{2 -}$ . Hence, its vant hoff factor is 3.

Therefore, the ratio of depression of freezing point will be the ratio of their vant hoff factor because the molarity is same for all three solution. The ratio will be 2 : 2 : 3. Further divided, the ratio will be 1 : 1 : 1.5

544.

Which of the following pairs of substances cannot exist together in solution?

Na₂CO₃ + NaOH
NaHCO₃ + Na₂CO₃
NaHCO₃ + NaOH
NaOH + HCl

545.

Assertion : Azeotropic mixtures are formed only by non-ideal solutions and they may have boiling points either greater than both the components or lesser than both the components.

Reason : The composition of the vapour phase is same as that ofthe liquid phase of an azeotropic mixture.

If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false
If both assertion and reason are false.

546.

Large difference in boiling points is observed in

N and P
P and As
As and Sb
Sb and Bi

547.

Arrange the given compounds in decreasing order of boiling points.

I. CH₃CH₂CH₂CH₂Br

II. C(CH₃)₃Br

III. CH₃-CH₂-CH(CH₃)-Br

I > III > II
II > I > III
I > II > III
III > I > II

548.

Two elements A and B form compounds of formula AB₂ and AB₄. When dissolved in 20.0 g of benzene 1.0 g of AB₂ lowers freezing point by 2.3°C whereas 1.0 g of AB₄ lowers freezing point by 1.3°C. The K_f for benzene is 5.1. The atomic masses of A and B are

25, 42
42, 25
52, 48
48, 52

549.

The freezing point of a solution containing 0.2 g of acetic acid in 20.0 g benzene is lowered by 0.45°C. The degree of association of acetic acid in benzene is (Assume acetic acid dimerises in benzene and K_f for benzene = 5.12K kg mol^-1) M_observed of acetic acid = 113.78