CBQ Practice›Class 12 Chemistry
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Class 12 Chemistry
CBQ Practice

Competency Based Questions · 3 chapters · 6 CBQ sets

Question types:Case StudySource BasedAssertion–Reason
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Ch 2

Solutions

2 sets
CBQ 1Case StudyColligative Properties in Everyday Life4 marks

Read the passage

In cold regions, salt (NaCl) is spread on icy roads. The salt dissolves in the surface water, forming a saline solution. This solution has a lower freezing point than pure water — a phenomenon called 'depression in freezing point', which is a colligative property. The depression in freezing point (ΔTf) is given by ΔTf = Kf × m, where Kf is the cryoscopic constant and m is the molality of the solution. Similarly, when cooking vegetables, salt is added to water — the boiling point increases (elevation in boiling point). These properties depend only on the number of solute particles, not their nature. A chemistry student uses these concepts to determine the molar mass of an unknown solute by measuring ΔTf.
1

Depression in freezing point is a colligative property because it depends on:

1M
(A)The nature and size of solute molecules
(B)The number of solute particles present in the solution
(C)The colour of the solute
(D)The chemical reactivity of the solute
2

The formula for depression in freezing point is ΔTf = Kf × m. Here, m represents:

1M
(A)Molarity of the solution
(B)Mass of solute in grams
(C)Molality of the solution (moles of solute per kg of solvent)
(D)Mole fraction of solute
3

Adding salt to icy roads works because:

1M
(A)Salt generates heat and melts ice
(B)The saline solution has a lower freezing point than pure water
(C)Salt absorbs moisture from ice
(D)Salt increases the density of ice
4

18 g of glucose (M = 180 g/mol) is dissolved in 1 kg of water. Calculate ΔTf if Kf (water) = 1.86 K kg/mol.

1M
CBQ 2Assertion–Reason1 mark
A
Assertion

The osmotic pressure of a 0.1 M NaCl solution is greater than the osmotic pressure of a 0.1 M glucose solution at the same temperature.

R
Reason

NaCl is a strong electrolyte that dissociates into two ions (Na⁺ and Cl⁻), effectively doubling the number of solute particles compared to glucose, which does not dissociate.

(A) Both A and R are true and R is the correct explanation of A
(B) Both A and R are true but R is not the correct explanation of A
(C) A is true but R is false
(D) A is false but R is true
Ch 3

Electrochemistry

2 sets
CBQ 1Case StudyThe Daniell Cell4 marks

Read the passage

A Daniell cell is a classic galvanic cell consisting of a zinc electrode immersed in zinc sulphate (ZnSO₄) solution and a copper electrode in copper sulphate (CuSO₄) solution, connected by a salt bridge. The two half-cells are: Zn → Zn²⁺ + 2e⁻ (anode, oxidation) and Cu²⁺ + 2e⁻ → Cu (cathode, reduction). The standard electrode potentials are: E°(Zn²⁺/Zn) = −0.76 V and E°(Cu²⁺/Cu) = +0.34 V. The standard cell potential E°cell = E°cathode − E°anode. The salt bridge maintains electrical neutrality by allowing ions to flow between the two solutions. The EMF of the cell can be calculated using the Nernst equation when concentrations are non-standard.
1

In the Daniell cell, oxidation occurs at the:

1M
(A)Copper electrode (cathode)
(B)Zinc electrode (anode)
(C)Salt bridge
(D)External circuit
2

The standard cell potential E°cell for the Daniell cell is:

1M
(A)−1.10 V
(B)+0.42 V
(C)+1.10 V
(D)−0.42 V
3

The function of the salt bridge in a galvanic cell is:

1M
(A)To allow electron flow between the two half-cells
(B)To maintain electrical neutrality by allowing ion flow between the two solutions
(C)To increase the EMF of the cell
(D)To prevent the reaction from occurring
4

Write the Nernst equation for the Daniell cell and state what happens to E_cell when the concentration of Zn²⁺ is increased.

1M
CBQ 2Assertion–Reason1 mark
A
Assertion

Conductivity of a strong electrolyte solution decreases with dilution.

R
Reason

On dilution, the number of ions per unit volume decreases, reducing the ability of the solution to conduct electricity.

(A) Both A and R are true and R is the correct explanation of A
(B) Both A and R are true but R is not the correct explanation of A
(C) A is true but R is false
(D) A is false but R is true
Ch 4

Chemical Kinetics

2 sets
CBQ 1Case StudyDecomposition of N₂O₅4 marks

Read the passage

The decomposition of dinitrogen pentoxide (N₂O₅) in carbon tetrachloride solvent is a first-order reaction: 2N₂O₅ → 4NO₂ + O₂. A chemist monitors the reaction at 45°C. At time t = 0, the concentration of N₂O₅ is 2.0 × 10⁻² mol/L. After 30 minutes, it becomes 1.0 × 10⁻² mol/L. The chemist notes that for a first-order reaction, the half-life t₁/₂ = 0.693/k is constant and independent of the initial concentration. The rate constant k can be calculated from integrated first-order rate law: k = (2.303/t) log ([A]₀/[A]). The Arrhenius equation k = A·e^(−Ea/RT) shows how k varies with temperature.
1

For a first-order reaction, the half-life is:

1M
(A)Directly proportional to the initial concentration
(B)Inversely proportional to the initial concentration
(C)Independent of the initial concentration
(D)Equal to the rate constant
2

From the data given (concentration halved in 30 minutes), the half-life of the reaction is:

1M
(A)15 min
(B)30 min
(C)60 min
(D)45 min
3

According to the Arrhenius equation, the rate constant k increases with temperature because:

1M
(A)Higher temperature decreases the activation energy
(B)Higher temperature increases the fraction of molecules having energy equal to or greater than the activation energy
(C)Higher temperature decreases the collision frequency
(D)Higher temperature increases the activation energy
4

Calculate the rate constant k for the decomposition of N₂O₅ given that the half-life is 30 minutes.

1M
CBQ 2Assertion–Reason1 mark
A
Assertion

Increasing the temperature by 10°C approximately doubles the rate of a chemical reaction.

R
Reason

A 10°C rise in temperature roughly doubles the fraction of molecules possessing energy greater than or equal to the activation energy, as described by the Arrhenius equation.

(A) Both A and R are true and R is the correct explanation of A
(B) Both A and R are true but R is not the correct explanation of A
(C) A is true but R is false
(D) A is false but R is true

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