NUMS — Medical & Dental Entry Test

NUMS Chemistry — Kinetics, Acids and Bases, Electrochemistry (Set 5)

Take the NUMS Chemistry — Kinetics, Acids and Bases, Electrochemistry (Set 5): 30 multiple-choice questions (40 minutes) with instant scoring and a full…

What this test covers

30 NUMS Chemistry

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

Q1. For A + B → products, initial rates were: (1) [A] = 0.10 M, [B] = 0.10 M, rate = 2.0 × 10⁻⁴ M s⁻¹; (2) [A] = 0.20 M, [B] = 0.10 M, rate = 8.0 × 10⁻⁴ M s⁻¹; (3) [A] = 0.10 M, [B] = 0.30 M, rate = 6.0 × 10⁻⁴ M s⁻¹. What is the rate constant?
- A. 0.20 M⁻¹ s⁻¹
- B. 2.0 × 10⁻² M⁻² s⁻¹
- C. 2.0 M⁻² s⁻¹
- D. 0.20 M⁻² s⁻¹ ✓
Answer: D. 0.20 M⁻² s⁻¹
Explanation: Doubling [A] quadruples the rate (second order in A); tripling [B] triples it (first order in B). Rate = k[A]²[B], so k = 2.0 × 10⁻⁴/(0.10² × 0.10) = 0.20 M⁻² s⁻¹.
Q2. A reaction has k = 1.00 × 10⁻³ s⁻¹ at 300 K and activation energy 80.0 kJ mol⁻¹ (frequency factor constant). What is k at 320 K? (R = 8.314 J mol⁻¹ K⁻¹)
- A. 2.0 × 10⁻³ s⁻¹
- B. 1.6 × 10⁻² s⁻¹
- C. 7.4 × 10⁻³ s⁻¹ ✓
- D. 4.0 × 10⁻³ s⁻¹
Answer: C. 7.4 × 10⁻³ s⁻¹
Explanation: ln(k₂/k₁) = (Eₐ/R)(1/T₁ − 1/T₂) = (80 000/8.314)(1/300 − 1/320) = 2.004, so k₂ = 1.00 × 10⁻³ × e^2.004 = 7.4 × 10⁻³ s⁻¹.
Q3. For a second-order reaction 2A → products, k = 0.50 M⁻¹ s⁻¹ and [A]₀ = 0.20 M. What is [A] after 20 s? (Use 1/[A] = 1/[A]₀ + kt.)
- A. 0.020 M
- B. 0.067 M ✓
- C. 0.10 M
- D. 0.18 M
Answer: B. 0.067 M
Explanation: 1/[A] = 1/0.20 + 0.50 × 20 = 5.0 + 10.0 = 15.0 M⁻¹, so [A] = 0.067 M.
Q4. A drug is eliminated from the blood by a first-order process with a half-life of 4.0 h. What fraction of the dose remains 10 h after it was given (no further doses)?
- A. 0.250
- B. 0.125
- C. 0.177 ✓
- D. 0.0625
Answer: C. 0.177
Explanation: Number of half-lives = 10/4.0 = 2.5. Fraction = (½)^2.5 = 0.177. (Naively using 2 or 3 half-lives gives 0.25 or 0.125.)
Q5. The decomposition of hydrogen peroxide catalysed by iodide proceeds by: (1) H₂O₂ + I⁻ → H₂O + IO⁻ (slow); (2) H₂O₂ + IO⁻ → H₂O + O₂ + I⁻ (fast). Which of the following correctly identifies the catalyst and the intermediate?
- A. Catalyst: I⁻; intermediate: IO⁻ ✓
- B. Catalyst: I⁻; intermediate: O₂
- C. Catalyst: H₂O; intermediate: IO⁻
- D. Catalyst: IO⁻; intermediate: I⁻
Answer: A. Catalyst: I⁻; intermediate: IO⁻
Explanation: I⁻ is consumed in step 1 and regenerated in step 2, so it is the catalyst. IO⁻ is formed in step 1 and used up in step 2, so it is an intermediate.

The other 25 questions

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Q6. What is the pH of 0.010 M barium hydroxide solution at 25 °C, assuming complete dissociation?
- A. 2.00
- B. 12.00
- C. 11.70
- D. 12.30
Q7. What is the pH of 1.0 × 10⁻⁸ M HCl at 25 °C when the ionisation of water is properly taken into account?
- A. 7.00
- B. 6.00
- C. 6.98
- D. 8.00
Q8. A 0.10 M solution of a weak monoprotic acid HA has a pH of 3.00. What is Ka of the acid?
- A. 1.0 × 10⁻⁶
- B. 1.0 × 10⁻⁴
- C. 1.0 × 10⁻³
- D. 1.0 × 10⁻⁵
Q9. A 1.0 L buffer contains 0.20 mol NH₃ and 0.10 mol NH₄Cl (pKb of NH₃ = 4.74 at 25 °C). About what is its pH after 0.010 mol of HCl is added (no volume change)?
- A. 9.50
- B. 8.96
- C. 9.56
- D. 9.62
Q10. 25.0 mL of 0.100 M acetic acid (Ka = 1.8 × 10⁻⁵) is titrated with 0.100 M NaOH. What is the pH at the equivalence point?
- A. 4.74
- B. 8.72
- C. 7.00
- D. 9.26
Q11. What is the pH of 0.10 M NH₄Cl solution? (Kb of NH₃ = 1.8 × 10⁻⁵; Kw = 1.0 × 10⁻¹⁴)
- A. 5.13
- B. 8.87
- C. 2.87
- D. 7.00
Q12. 0.10 M acetic acid (Ka = 1.8 × 10⁻⁵) is made 0.10 M in added HCl. Taking [H⁺] ≈ 0.10 M, what is the acetate ion concentration?
- A. 0.10 M
- B. 1.3 × 10⁻³ M
- C. 1.8 × 10⁻⁵ M
- D. 1.8 × 10⁻² M
Q13. A cell is made of Cu | Cu²⁺ (1.0 M) ‖ Ag⁺ (0.0010 M) | Ag, with E°(Ag⁺/Ag) = +0.80 V and E°(Cu²⁺/Cu) = +0.34 V. Using E = E° − (0.0592/n) log Q at 25 °C, what is the cell emf?
- A. 0.46 V
- B. 0.64 V
- C. 0.10 V
- D. 0.28 V
Q14. The Daniell cell has E° = 1.10 V for Zn + Cu²⁺ → Zn²⁺ + Cu (n = 2). What is ΔG° for the reaction? (F = 96 485 C mol⁻¹)
- A. −106 kJ mol⁻¹
- B. +212 kJ mol⁻¹
- C. −212 kJ mol⁻¹
- D. −1.10 kJ mol⁻¹
Q15. A steady current of 2.00 A is passed through dilute sulphuric acid between inert electrodes for 965 s. What is the total volume of gases (H₂ + O₂) liberated at STP? (F = 96 500 C mol⁻¹; molar volume 22.4 L mol⁻¹)
- A. 112 mL
- B. 224 mL
- C. 448 mL
- D. 336 mL
Q16. Aqueous CuSO₄ is electrolysed using impure copper as the anode and pure copper as the cathode. What happens at the electrodes?
- A. Anode copper dissolves; hydrogen is released at the cathode
- B. Oxygen is released at the anode; copper deposits on the cathode
- C. Oxygen is released at the anode; hydrogen at the cathode
- D. Anode copper dissolves; copper deposits on the cathode
Q17. E° values: Fe³⁺/Fe²⁺ = +0.77 V, I₂/I⁻ = +0.54 V, Br₂/Br⁻ = +1.07 V. Which statement is correct under standard conditions?
- A. Fe³⁺ oxidises Br⁻ but not I⁻
- B. Fe³⁺ oxidises both I⁻ and Br⁻
- C. Fe³⁺ oxidises I⁻ but not Br⁻
- D. Fe³⁺ oxidises neither I⁻ nor Br⁻
Q18. Chromium pentoxide, CrO₅, has one Cr=O bond and two peroxide (O–O) groups. What is the oxidation number of chromium in it?
- A. +10
- B. +3
- C. +6
- D. +5
Q19. In acid solution, 25.0 mL of 0.0200 M K₂Cr₂O₇ exactly oxidises Fe²⁺ in 20.0 mL of a solution (Cr₂O₇²⁻ + 14H⁺ + 6Fe²⁺ → 2Cr³⁺ + 6Fe³⁺ + 7H₂O). What is [Fe²⁺]?
- A. 0.900 M
- B. 0.150 M
- C. 0.0500 M
- D. 0.0250 M
Q20. In an acidic hydrogen–oxygen fuel cell, which half-reaction occurs at the anode?
- A. O₂ + 4H⁺ + 4e⁻ → 2H₂O
- B. H₂ → 2H⁺ + 2e⁻
- C. 2H₂O → O₂ + 4H⁺ + 4e⁻
- D. 2H⁺ + 2e⁻ → H₂
Q21. The limiting molar conductivities (S cm² mol⁻¹) at 25 °C are HCl 426, NaCH₃COO 91 and NaCl 126. What is Λ° for acetic acid?
- A. 643
- B. 217
- C. 391
- D. 461
Q22. An iron sheet is coated with tin in one case and with zinc in another. In each case the coating is scratched so that iron is exposed to moist air. Which statement is correct?
- A. Iron rusts at the same rate under both coatings
- B. Iron rusts faster under tin and is protected by zinc
- C. Iron is protected by both coatings
- D. Iron rusts faster under zinc and is protected by tin
Q23. In a working zinc–copper galvanic cell with a KNO₃ salt bridge, in which directions do the electrons (in the wire) and the NO₃⁻ ions (in the bridge) move?
- A. Electrons Cu → Zn; NO₃⁻ toward the zinc half-cell
- B. Electrons Cu → Zn; NO₃⁻ toward the copper half-cell
- C. Electrons Zn → Cu; NO₃⁻ toward the copper half-cell
- D. Electrons Zn → Cu; NO₃⁻ toward the zinc half-cell
Q24. A hydrogen electrode (H₂ at 1 atm) is dipped in a solution of pH 7.00 at 25 °C. Using E = E° − (0.0592/2) log(1/[H⁺]²) for 2H⁺ + 2e⁻ → H₂ (E° = 0), what is its electrode potential?
- A. 0.000 V
- B. +0.414 V
- C. −0.828 V
- D. −0.414 V
Q25. Two copper electrodes dip into CuSO₄ solutions of 0.010 M and 1.00 M joined by a salt bridge. Using E = E° − (0.0592/n) log Q at 25 °C, what is the cell emf?
- A. 0.030 V
- B. 0.059 V
- C. 0.118 V
- D. 0.34 V
Q26. The rate of a reaction doubles for every 10 K rise in temperature. By what factor is the rate larger at 330 K than at 300 K?
- A. 3
- B. 6
- C. 8
- D. 32
Q27. A first-order reaction is 75% complete in 40.0 min. What is its rate constant?
- A. 2.50 × 10⁻² min⁻¹
- B. 3.47 × 10⁻² min⁻¹
- C. 1.73 × 10⁻² min⁻¹
- D. 6.93 × 10⁻² min⁻¹
Q28. 100 mL of HCl of pH 2.00 is mixed with 100 mL of HCl of pH 4.00. What is the pH of the mixture?
- A. 2.70
- B. 2.00
- C. 3.00
- D. 2.30
Q29. The conjugate acid of ammonia, NH₄⁺, has pKa = 9.25 at 25 °C. What is pKb for NH₃? (pKw = 14.00)
- A. 4.75
- B. −4.75
- C. 14.00
- D. 9.25
Q30. The same charge is passed through two cells in series, one containing AgNO₃ solution and one containing CuSO₄ solution. If 1.08 g of silver (Ag = 108) is deposited, what mass of copper (Cu = 63.5) is deposited?
- A. 1.08 g
- B. 0.159 g
- C. 0.318 g
- D. 0.635 g