NEET MCQs: Molar-mass determination, abnormal molar mass and van’t Hoff factor

Question 1

Which of the following colligative properties is most commonly used for the determination of the molar mass of polymers and biomolecules like proteins?

Accepted Answer

Osmotic pressure

Answer

Depression in freezing point

Answer

Elevation in boiling point

Answer

Relative lowering of vapour pressure

Question 2

Assuming complete dissociation of any electrolyte, the depression in freezing point of a 0.25 molal aqueous solution of K₂SO₄ is (K_f of water = 1.86 K kg mol⁻¹):

Accepted Answer

1.4 K

Answer

1.86 K

Answer

7.44 K

Answer

0.465 K

Question 3

A compound with normal molar mass of 244 g mol⁻¹ dissolves in an organic solvent and undergoes association: 2B ⇌ B₂. When 2.44 g of this solute is dissolved in 50 g of the solvent (K_f = 5.0 K kg mol⁻¹), the observed depression in freezing point is 0.60 K. What is the percentage association of the compound in this solvent?

Accepted Answer

80%

Answer

60%

Answer

75%

Answer

40%

Question 4

The freezing point of an aqueous solution containing 0.05 mol kg⁻¹ of a weak acid HX is -0.106 °C. Calculate the van’t Hoff factor (i) and the degree of dissociation (α) of the acid. (K_f for water = 1.86 K kg mol⁻¹)

Accepted Answer

i = 1.14, α = 0.14

Answer

i = 1.28, α = 0.28

Answer

i = 1.07, α = 0.07

Answer

i = 1.20, α = 0.20

Question 5

Which of the following pairs of 0.10 mol kg⁻¹ aqueous solutions will have the identical elevation in boiling point, assuming complete dissociation of all ionic solutes?

Accepted Answer

CaCl₂ and K₂SO₄

Answer

NaCl and Na₂SO₄

Answer

AlCl₃ and K₄[Fe(CN)₆]

Answer

FeCl₃ and BaCl₂

Question 6

An aqueous solution contains a complex represented by Co(NH₃)₄Cl₃. A 0.01 m aqueous solution of this complex freezes at -0.0372 °C. Assuming 100% ionization of the complex and K_f for water = 1.86 K kg mol⁻¹, what is the correct coordination formula of the complex?

Accepted Answer

[Co(NH₃)₄Cl₂]Cl

Answer

[Co(NH₃)₄]Cl₃

Answer

[Co(NH₃)₄Cl]Cl₂

Answer

[Co(NH₃)₄Cl₃]

Question 7

Assuming complete dissociation of any electrolyte, the depression in freezing point of a 0.2 molal aqueous solution of NaCl is (K_f of water = 1.86 K kg mol⁻¹):

Accepted Answer

0.744 K

Answer

1.12 K

Answer

0.372 K

Answer

9.3 K

Question 8

Given below are two statements:
Statement I: The abnormal molar mass determined from colligative properties is always greater than the normal molar mass when the solute dissociates in the solution.
Statement II: Dissociation of solute particles leads to an increase in the total number of particles, which causes an increase in the observed value of colligative properties.
In light of the above statements, choose the correct answer:

Accepted Answer

Statement I is incorrect but Statement II is correct

Answer

Both Statement I and Statement II are correct

Answer

Statement I is correct but Statement II is incorrect

Answer

Both Statement I and Statement II are incorrect

Question 9

Assuming complete dissociation of any electrolyte, the depression in freezing point of a 0.25 molal aqueous solution of CaCl₂ is (K_f of water = 1.86 K kg mol⁻¹):

Accepted Answer

1.4 K

Answer

7.44 K

Answer

1.86 K

Answer

0.465 K

Question 10

Assuming complete dissociation of any electrolyte, the depression in freezing point of a 0.5 molal aqueous solution of K₂SO₄ is (K_f of water = 1.86 K kg mol⁻¹):

Accepted Answer

2.79 K

Answer

5.58 K

Answer

3.72 K

Answer

0.93 K

Question 11

A 0.1 m solution of a weak monobasic acid HA has a freezing point of -0.2046 °C. If the cryoscopic constant (K_f) of water is 1.86 K kg mol⁻¹, the degree of dissociation (α) of the acid is:

Accepted Answer

0.10

Answer

0.05

Answer

0.15

Answer

0.20

Question 12

Assuming complete dissociation of any electrolyte, the depression in freezing point of a 1 molal aqueous solution of urea is (K_f of water = 1.86 K kg mol⁻¹):

Accepted Answer

1.86 K

Answer

0.93 K

Answer

3.72 K

Answer

2.79 K

Molar-mass determination, abnormal molar mass and van’t Hoff factor: NEET MCQs with answers

1. Which of the following colligative properties is most commonly used for the determination of the molar mass of polymers and biomolecules like proteins?

2. Assuming complete dissociation of any electrolyte, the depression in freezing point of a 0.25 molal aqueous solution of K₂SO₄ is (K_f of water = 1.86 K kg mol⁻¹):

4. The freezing point of an aqueous solution containing 0.05 mol kg⁻¹ of a weak acid HX is -0.106 °C. Calculate the van’t Hoff factor (i) and the degree of dissociation (α) of the acid. (K_f for water = 1.86 K kg mol⁻¹)

5. Which of the following pairs of 0.10 mol kg⁻¹ aqueous solutions will have the identical elevation in boiling point, assuming complete dissociation of all ionic solutes?

6. An aqueous solution contains a complex represented by Co(NH₃)₄Cl₃. A 0.01 m aqueous solution of this complex freezes at -0.0372 °C. Assuming 100% ionization of the complex and K_f for water = 1.86 K kg mol⁻¹, what is the correct coordination formula of the complex?

7. Assuming complete dissociation of any electrolyte, the depression in freezing point of a 0.2 molal aqueous solution of NaCl is (K_f of water = 1.86 K kg mol⁻¹):

9. Assuming complete dissociation of any electrolyte, the depression in freezing point of a 0.25 molal aqueous solution of CaCl₂ is (K_f of water = 1.86 K kg mol⁻¹):

10. Assuming complete dissociation of any electrolyte, the depression in freezing point of a 0.5 molal aqueous solution of K₂SO₄ is (K_f of water = 1.86 K kg mol⁻¹):

11. A 0.1 m solution of a weak monobasic acid HA has a freezing point of -0.2046 °C. If the cryoscopic constant (K_f) of water is 1.86 K kg mol⁻¹, the degree of dissociation (α) of the acid is:

12. Assuming complete dissociation of any electrolyte, the depression in freezing point of a 1 molal aqueous solution of urea is (K_f of water = 1.86 K kg mol⁻¹):

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