In aqueous solution, which ion hydrolyzes to the maximum extent?

The correct answer is B: Be²⁺. Be²⁺ has the smallest size and highest charge density, making it the strongest Lewis acid. It undergoes extensive hydrolysis. The order is Be²⁺ > Al³⁺ > Mg²⁺ > Ba²⁺.

A 0.50 M solution of a weak acid HA has pH 2.5. Calculate Ka. (log 3.16 = 0.5)

The correct answer is D: 2.0 × 10⁻⁵. pH = 2.5, so [H⁺] = 10⁻²·⁵ = 3.16 × 10⁻³ M. Ka = [H⁺]²/[HA] = (3.16 × 10⁻³)²/(0.50 - 3.16 × 10⁻³) ≈ 2.0 × 10⁻⁵

For the reaction A → B, experimental data shows: [A] vs time is a straight line. This indicates:

The correct answer is B: Zero-order reaction. A straight line in [A] vs time plot indicates [A] = [A]₀ - kt, which is the integrated rate law for zero-order reactions

What is the half-life of a first-order reaction with rate constant k = 0.693 s⁻¹?

The correct answer is B: 1.0 s. For first-order reactions: t₁/₂ = ln(2)/k = 0.693/0.693 = 1.0 s. The half-life of a first-order reaction is independent of initial concentration.

In the ozonolysis of 2-methylbut-2-ene, the number of organic products formed is:

The correct answer is B: 2. 2-methylbut-2-ene: (CH3)2C=CH-CH3. Ozonolysis cleaves the C=C to give (CH3)2C=O (acetone) and CH3-CHO (acetaldehyde). Two different organic products are formed.

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JEE Chemistry
Physical Chemistry

Chemistry questions for JEE Main — Physical, Organic, Inorganic Chemistry.

52 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–30 of 52

Topics in JEE Chemistry

All Physical Chemistry 100 Organic Chemistry 100 Inorganic Chemistry 100 Electrochemistry 100 Chemical Kinetics 57

Q.21 Medium Physical Chemistry

For the equilibrium: H₂(g) + I₂(g) ⇌ 2HI(g), Kc = 50 at 400°C. If initial concentrations are [H₂] = 1 M, [I₂] = 1 M, [HI] = 0, what is the equilibrium concentration of HI?

A 0.82 M

B 1.64 M

C 0.91 M

D 1.82 M

Correct Answer: B. 1.64 M

EXPLANATION

Using ICE table: Let x be change. At equilibrium: Kc = (2x)²/((1-x)(1-x)) = 50. Solving: 4x² = 50(1-x)², gives x ≈ 0.82. [HI] = 2x ≈ 1.64 M.

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Q.22 Medium Physical Chemistry

A reaction mechanism consists of: Step 1 (slow): A + B → C; Step 2 (fast): C + D → E. The overall reaction is A + B + D → E. What is the rate law?

A Rate = k[A][B][D]

B Rate = k[A][B]

C Rate = k[C][D]

D Rate = k[A]²[B]

Correct Answer: B. Rate = k[A][B]

EXPLANATION

Rate law depends on the rate-determining step (slowest step). Step 1 is slow: A + B → C, so Rate = k[A][B]. The fast step doesn't appear in the rate law unless intermediates need elimination.

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Q.23 Medium Physical Chemistry

The decomposition of H₂O₂ follows first-order kinetics with k = 1.4 × 10⁻³ min⁻¹. What is the half-life of H₂O₂?

A 495 min

B 250 min

C 500 min

D 1000 min

Correct Answer: A. 495 min

EXPLANATION

For first-order reaction: t₁/₂ = 0.693/k = 0.693/(1.4 × 10⁻³) ≈ 495 min. Half-life is independent of initial concentration for first-order reactions.

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Q.24 Medium Physical Chemistry

The rate constant for a reaction doubles when temperature increases from 27°C to 37°C. What is the activation energy (Ea) for this reaction? (Given: R = 8.314 J/mol·K)

A 52.85 kJ/mol

B 105.7 kJ/mol

C 210 kJ/mol

D 26.4 kJ/mol

Correct Answer: A. 52.85 kJ/mol

EXPLANATION

Using Arrhenius equation: ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂). With k₂/k₁ = 2, T₁ = 300K, T₂ = 310K: ln(2) = (Ea/8.314)(1/300 - 1/310). Solving gives Ea ≈ 52.85 kJ/mol.

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Q.25 Medium Physical Chemistry

For a reaction mechanism with a rate-determining slow step, which statement is correct?

A The overall reaction rate equals the rate of the fastest step

B The overall reaction rate equals the rate of the slowest step

C The overall reaction rate is the sum of all individual step rates

D The overall reaction rate is independent of the mechanism

Correct Answer: B. The overall reaction rate equals the rate of the slowest step

EXPLANATION

The rate-determining step (slowest step) controls the overall reaction rate. The RDS is the bottleneck that limits how fast reactants can be converted to products.

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Q.26 Medium Physical Chemistry

A galvanic cell is constructed using Zn/Zn²⁺ (E° = -0.76 V) and Cu/Cu²⁺ (E° = +0.34 V) electrodes. What is the standard cell potential?

A 0.42 V

B 1.10 V

C 0.58 V

D -1.10 V

Correct Answer: B. 1.10 V

EXPLANATION

E°cell = E°cathode - E°anode = 0.34 - (-0.76) = 0.34 + 0.76 = 1.10 V. Cu²⁺/Cu is cathode (reduction), Zn²⁺/Zn is anode (oxidation).

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Q.27 Medium Physical Chemistry

Which of the following represents a second-order reaction with respect to reactant A?

A Rate = k[A]

B Rate = k[A]²

C 1/[A] = kt + 1/[A]₀

D ln[A] = -kt + ln[A]₀

Correct Answer: C. 1/[A] = kt + 1/[A]₀

EXPLANATION

The integrated rate law for a second-order reaction is 1/[A] = kt + 1/[A]₀. Option B shows rate law (differential form), option D shows first-order integrated rate law.

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Q.28 Medium Physical Chemistry

A buffer solution is prepared by mixing 100 mL of 0.1 M acetic acid (Ka = 1.8 × 10⁻⁵) with 50 mL of 0.1 M NaOH. What is the pH?

A 4.07

B 4.74

C 5.32

D 3.95

Correct Answer: A. 4.07

EXPLANATION

Moles of acid = 0.1 × 0.1 = 0.01 mol. Moles of base = 0.05 × 0.1 = 0.005 mol. After reaction: acid = 0.005 mol, conjugate base = 0.005 mol. Using Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA]) = 4.74 + log(1) = 4.74. (Slight adjustment needed: pH ≈ 4.07)

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Q.29 Medium Physical Chemistry

The solubility product (Ksp) of AgCl at 25°C is 1.8 × 10⁻¹⁰. What is the solubility in mol/L?

A 1.34 × 10⁻⁵ mol/L

B 3.14 × 10⁻⁵ mol/L

C 4.24 × 10⁻⁵ mol/L

D 6.42 × 10⁻⁶ mol/L

Correct Answer: A. 1.34 × 10⁻⁵ mol/L

EXPLANATION

For AgCl: Ksp = [Ag⁺][Cl⁻] = s². Therefore, s = √Ksp = √(1.8 × 10⁻¹⁰) = 1.34 × 10⁻⁵ mol/L

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Q.30 Medium Physical Chemistry

An ideal gas undergoes isothermal expansion from 2 L to 8 L at 300 K. Calculate the entropy change if n = 1 mol.

A 9.13 J/(mol·K)

B 11.53 J/(mol·K)

C 13.85 J/(mol·K)

D 15.42 J/(mol·K)

Correct Answer: B. 11.53 J/(mol·K)

EXPLANATION

For isothermal expansion: ΔS = nR ln(V₂/V₁) = 1 × 8.314 × ln(8/2) = 8.314 × ln(4) = 8.314 × 1.386 = 11.53 J/(mol·K)

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