NUMS — Medical & Dental Entry Test
Take the NUMS Chemistry — Kinetics, Acids and Bases, Electrochemistry (Set 7): 30 multiple-choice questions (40 minutes) with instant scoring and a full…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. A first-order reaction has k = 2.303 × 10⁻³ s⁻¹. How long does it take for 99% of the reactant to be consumed?
Answer: B. 2000 s
Explanation: t = (2.303/k) log([A]₀/[A]) = (2.303/2.303 × 10⁻³) × log 100 = 1000 × 2 = 2000 s.
Q2. The rate constant of a reaction doubles when the temperature is raised from 300 K to 310 K. Using ln(k₂/k₁) = (Eₐ/R)(1/T₁ − 1/T₂) with R = 8.314 J K⁻¹ mol⁻¹, what is the activation energy?
Answer: D. 53.6 kJ mol⁻¹
Explanation: Eₐ = R ln2/(1/300 − 1/310) = 8.314 × 0.693/(1.075 × 10⁻⁴) = 53.6 kJ mol⁻¹.
Q3. A second-order reaction 2A → products has k = 0.10 dm³ mol⁻¹ s⁻¹ and [A]₀ = 0.50 mol dm⁻³. What is [A] after 20 s? (1/[A] = 1/[A]₀ + kt)
Answer: B. 0.25 mol dm⁻³
Explanation: 1/[A] = 2.0 + 0.10 × 20 = 4.0 dm³ mol⁻¹, so [A] = 0.25 mol dm⁻³.
Q4. A zero-order reaction has k = 0.020 mol dm⁻³ s⁻¹ and an initial concentration of 0.80 mol dm⁻³. How long does it take for the reactant to be completely consumed?
Answer: C. 40 s
Explanation: For zero order [A] = [A]₀ − kt, so t = 0.80/0.020 = 40 s. (The half-life is 20 s but the reaction finishes in twice that.)
Q5. In two experiments the initial rate of A + B → products is measured. Doubling [A] with [B] fixed multiplies the rate by 4; doubling [B] with [A] fixed multiplies the rate by 2. What is the overall order of reaction?
Answer: C. 3
Explanation: Order in A is 2 (2² = 4) and in B is 1 (2¹ = 2); rate = k[A]²[B], overall order = 3.
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Q6. What is the pH of 0.10 M NH₄Cl, given Kb(NH₃) = 1.8 × 10⁻⁵ and Kw = 1.0 × 10⁻¹⁴? (Treat NH₄⁺ as a weak acid and ignore water's ionisation.)
Q7. A buffer is made with 0.10 mol CH₃COOH and 0.05 mol CH₃COONa in 1.0 dm³ (Ka = 1.8 × 10⁻⁵). What is the pH after 0.010 mol of NaOH is added (no volume change)?
Q8. What volume of 0.15 M NaOH is needed to neutralise 25.0 cm³ of 0.10 M H₂SO₄?
Q9. 25.0 cm³ of 0.100 M CH₃COOH (Ka = 1.8 × 10⁻⁵) is titrated with 0.100 M NaOH. What is the pH at the equivalence point (25.0 cm³ of NaOH added)?
Q10. 1.0 cm³ of HCl of pH 2.0 is diluted with water to a final volume of 1.0 dm³. What is the pH of the diluted solution?
Q11. For how long must a current of 10.0 A be passed through molten Al₂O₃ to deposit 2.70 g of aluminium? (Al = 27, F = 96 500 C mol⁻¹)
Q12. A Daniell cell Zn | Zn²⁺(1.0 M) || Cu²⁺(0.010 M) | Cu has E°cell = 1.10 V at 25 °C. Using E = E° − (0.0592/n) log Q, what is its EMF?
Q13. Given E° (Fe³⁺/Fe²⁺) = +0.77 V and E° (I₂/I⁻) = +0.54 V, what is the standard EMF of the cell for 2Fe³⁺ + 2I⁻ → 2Fe²⁺ + I₂, and is the reaction spontaneous?
Q14. In 3MnO₄²⁻ + 4H⁺ → 2MnO₄⁻ + MnO₂ + 2H₂O, which statement is correct?
Q15. 10.0 cm³ of 0.100 M K₂Cr₂O₇ in acid solution oxidises Fe²⁺ to Fe³⁺ (Cr₂O₇²⁻ → 2Cr³⁺). What volume of 0.200 M FeSO₄ is oxidised?
Q16. A 0.0100 M solution of an electrolyte has a measured conductivity of 1.20 × 10⁻³ S cm⁻¹. What is its molar conductivity? (Λ = 1000κ/c)
Q17. Which of these ions is the weakest base?
Q18. An exothermic reaction has Eₐ(forward) = 100 kJ mol⁻¹ and Eₐ(reverse) = 130 kJ mol⁻¹. A catalyst lowers the forward activation energy to 70 kJ mol⁻¹. What are the new reverse activation energy and ΔH?
Q19. Assume the rate of a reaction doubles for every 10 °C rise in temperature. By what factor does the rate increase when the temperature is raised from 30 °C to 70 °C?
Q20. For a first-order reaction, a plot of ln[A] against time is a straight line of slope −0.050 min⁻¹. What is the half-life of the reaction?
Q21. An aqueous solution of CuSO₄ is electrolysed between two copper electrodes. Which statement is correct?
Q22. Given E° values Zn²⁺/Zn = −0.76 V, Fe²⁺/Fe = −0.44 V and Cu²⁺/Cu = +0.34 V, which solution can be stored in an iron container without reacting with it?
Q23. A solution of ammonium acetate, CH₃COONH₄, is almost exactly neutral (pH ≈ 7). What is the explanation?
Q24. The experimental rate law for 2NO(g) + 2H₂(g) → N₂(g) + 2H₂O(g) is rate = k[NO]²[H₂]. Which statement is correct?
Q25. In N₂ + 3H₂ → 2NH₃, ammonia forms at 0.60 mol dm⁻³ s⁻¹. At what rate is hydrogen consumed, and what is the rate of reaction as defined by the stoichiometric equation?
Q26. A hydrogen electrode (H₂ gas at 1 atm) is dipped into a solution of pH 3.0 at 25 °C. Using E = −0.0592 × pH volts for this half-cell, what is its electrode potential relative to the standard hydrogen electrode?
Q27. A 0.010 M solution of a weak monobasic acid HA has a pH of 4.0. What percentage of the acid is ionised?
Q28. The degree of dissociation of a weak electrolyte is 0.10 at a certain concentration. By what factor must the solution be diluted for the degree of dissociation to become 0.40? (Use Ostwald's dilution law with α ≪ 1.)
Q29. During the discharge of a lead–acid storage battery, what happens to the sulphuric acid electrolyte?
Q30. What quantity of charge is needed to reduce 0.100 mol of dichromate ions to Cr³⁺ in acid solution (Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O)? (F = 96 500 C mol⁻¹)