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Multiple Choice Questions

261.

The average molar heat capacity at constant volume of gaseous mixture contained 2 moles of each of two ideal gases X (C_V , m = $\frac{3}{2}$ R) and Y (C_V , m = $\frac{5}{2}$ R)

262.

How many grams of CaC₂O₄ will dissolve in distilled water to make one litre of saturated solution? Solubility product of CaC₂O₄ is 2.5 x 10^-9 mol² litre^-2 and its molecular weight is 128

0.0640 gm
0.0032 gm
0.0128 gm
0.0064 gm

263.

1 g of a non-volatile, non-electrolyte solute of molar mass 250 g/mol was dissolved in 51.2 g of benzene. If the freezing point depression constant , k_f of benzene is 5.12 kg K mol^-1 , the freezing point of benzene is lowered by :

0.3 K
0.5 K
0.2 K
0.4 K

264.

A 6% solution of urea is isotonic with :

1M solution of glucose
0.05 M solution of glucose
6% solution of glucose
25% solution of glucose

265.

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

266.

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

267.
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

268.

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

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

269.

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.