NUMS — Medical & Dental Entry Test

NUMS Chemistry — Kinetics, Acids and Bases, Electrochemistry (Set 2)

Take the NUMS Chemistry — Kinetics, Acids and Bases, Electrochemistry (Set 2): 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 the reaction A + B → products, doubling [A] alone makes the rate four times faster, while doubling [B] alone leaves the rate unchanged. What is the rate law?
- A. rate = k[A]²[B]
- B. rate = k[B]²
- C. rate = k[A]² ✓
- D. rate = k[A][B]
Answer: C. rate = k[A]²
Explanation: Rate ∝ [A]² (2² = 4) and is independent of [B] (zero order in B), so rate = k[A]².
Q2. The rate constant of a reaction has units of mol⁻¹ dm³ s⁻¹. What is the overall order of the reaction?
- A. Third order
- B. Second order ✓
- C. First order
- D. Zero order
Answer: B. Second order
Explanation: For order n, units of k are (mol dm⁻³)^(1−n) s⁻¹; mol⁻¹ dm³ s⁻¹ corresponds to 1 − n = −1, so n = 2.
Q3. For a zero-order reaction, how does the half-life change if the initial concentration of reactant is doubled?
- A. It becomes four times longer
- B. It halves
- C. It stays the same
- D. It doubles ✓
Answer: D. It doubles
Explanation: For zero order, t½ = [A]₀/2k, so the half-life is directly proportional to the initial concentration.
Q4. An enzyme lowers the activation energy of the forward step of a reversible reaction by 30 kJ mol⁻¹. What is its effect on the reverse step?
- A. Its activation energy is raised by 30 kJ mol⁻¹
- B. Its activation energy is unchanged
- C. The reverse reaction stops completely
- D. Its activation energy is also lowered by 30 kJ mol⁻¹ ✓
Answer: D. Its activation energy is also lowered by 30 kJ mol⁻¹
Explanation: A catalyst provides an alternative pathway with a lower energy barrier; the barrier is lowered equally for both directions, so ΔH and the position of equilibrium are unchanged.
Q5. According to collision theory, why does a small rise in temperature increase the rate of a reaction greatly?
- A. The total number of molecules increases
- B. The fraction of collisions with energy equal to or greater than the activation energy rises sharply ✓
- C. The activation energy decreases
- D. The reaction becomes more exothermic
Answer: B. The fraction of collisions with energy equal to or greater than the activation energy rises sharply
Explanation: Collision frequency rises only slightly; the main effect is that many more molecules in the Maxwell–Boltzmann distribution exceed Eₐ.

The other 25 questions

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Q6. A crushed antacid tablet neutralises stomach acid faster than a whole tablet of the same mass. Why?
- A. Crushing changes the chemical composition of the tablet
- B. Crushing increases the activation energy
- C. Crushing increases the surface area exposed to the acid
- D. Crushing raises the temperature of the acid
Q7. On a graph of reactant concentration against time, how is the instantaneous rate of reaction at a particular moment found?
- A. From the intercept on the concentration axis
- B. From the area under the curve
- C. From the slope of the tangent to the curve at that moment
- D. From the value of the concentration at that moment
Q8. In the decomposition 2N₂O₅ → 4NO₂ + O₂, N₂O₅ is consumed at 0.020 mol dm⁻³ s⁻¹. At what rate is O₂ formed?
- A. 0.005 mol dm⁻³ s⁻¹
- B. 0.010 mol dm⁻³ s⁻¹
- C. 0.020 mol dm⁻³ s⁻¹
- D. 0.040 mol dm⁻³ s⁻¹
Q9. A reaction's rate doubles when the temperature is raised from 300 K to 310 K. Using ln(k₂/k₁) = (Eₐ/R)(1/T₁ − 1/T₂), what is its activation energy? (R = 8.314 J K⁻¹ mol⁻¹, ln 2 = 0.693)
- A. 53.6 kJ mol⁻¹
- B. 107 kJ mol⁻¹
- C. 5.8 kJ mol⁻¹
- D. 0.53 kJ mol⁻¹
Q10. What is the pH of 0.005 M sulphuric acid, assuming both protons ionise completely?
- A. 3
- B. 1.7
- C. 2
- D. 2.3
Q11. 10 cm³ of hydrochloric acid of pH 2 is diluted with water to 1000 cm³. What is the pH of the diluted solution?
- A. 2
- B. 4
- C. 3
- D. 7
Q12. Four weak acids have the pKa values listed. Which acid is the strongest?
- A. Acid with pKa = 4.8
- B. Acid with pKa = 3.2
- C. Acid with pKa = 9.9
- D. Acid with pKa = 4.2
Q13. A weak acid HA has Ka = 1.0 × 10⁻⁵ at 25 °C. What is Kb of its conjugate base A⁻? (Kw = 1.0 × 10⁻¹⁴)
- A. 1.0 × 10⁻⁹
- B. 1.0 × 10⁻¹⁹
- C. 1.0 × 10⁹
- D. 1.0 × 10⁻⁵
Q14. A small amount of HCl is added to a buffer of ethanoic acid and sodium ethanoate. Why does the pH hardly change?
- A. The H⁺ ions evaporate as hydrogen gas
- B. The added H⁺ ions combine with ethanoate ions to form undissociated ethanoic acid
- C. The Na⁺ ions neutralise the added H⁺ ions
- D. Ethanoic acid ionises more to absorb the H⁺
Q15. According to Ostwald's dilution law, what happens to the degree of dissociation of a weak acid when its solution is diluted?
- A. It remains constant
- B. It increases
- C. It decreases
- D. It becomes zero
Q16. Which of the following species can act both as a Brønsted–Lowry acid and as a Brønsted–Lowry base?
- A. NH₄⁺
- B. Cl⁻
- C. CO₃²⁻
- D. HCO₃⁻
Q17. Which of these anions is the weakest base?
- A. Cl⁻
- B. F⁻
- C. CH₃COO⁻
- D. OH⁻
Q18. Aqueous ammonia is titrated with hydrochloric acid. Which statement about the equivalence point is correct?
- A. No indicator can detect the end point
- B. The pH is below 7, so methyl orange is a suitable indicator
- C. The pH is above 7, so phenolphthalein is a suitable indicator
- D. The pH is exactly 7, so any indicator works
Q19. 20.0 cm³ of sulphuric acid is exactly neutralised by 25.0 cm³ of 0.200 M NaOH. What is the concentration of the acid? (H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O)
- A. 0.125 M
- B. 0.250 M
- C. 0.0625 M
- D. 0.160 M
Q20. Sodium thiosulphate, Na₂S₂O₃, is used as an antidote in cyanide poisoning. What is the average oxidation number of sulphur in it?
- A. +2
- B. −2
- C. +6
- D. +4
Q21. Magnetite, Fe₃O₄, is an iron oxide. What is the average oxidation number of iron in it?
- A. +8/3
- B. +2
- C. +3
- D. +4/3
Q22. In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, which species acts as the oxidising agent?
- A. Zn²⁺
- B. Cu
- C. Cu²⁺
- D. Zn
Q23. In acidic solution, dichromate is reduced: Cr₂O₇²⁻ → 2Cr³⁺. How many electrons are gained per dichromate ion?
- A. 3
- B. 2
- C. 6
- D. 12
Q24. An aluminium strip in Al³⁺(aq) is connected through a salt bridge to a silver wire in Ag⁺(aq). E°(Al³⁺/Al) = −1.66 V and E°(Ag⁺/Ag) = +0.80 V. What is the standard emf of this cell?
- A. 4.06 V
- B. −2.46 V
- C. 2.46 V
- D. 0.86 V
Q25. An iron nail is placed in blue copper(II) sulphate solution. E°(Fe²⁺/Fe) = −0.44 V and E°(Cu²⁺/Cu) = +0.34 V. What happens?
- A. Iron deposits on copper ions
- B. Hydrogen gas is evolved from the solution
- C. No reaction occurs
- D. Copper deposits on the nail and iron dissolves as Fe²⁺
Q26. How much charge is needed to deposit 1 mol of aluminium from molten Al₂O₃ in cryolite? (F = 96 500 C mol⁻¹)
- A. 96 500 C
- B. 289 500 C
- C. 193 000 C
- D. 32 167 C
Q27. A current of 0.50 A is passed through copper(II) sulphate solution for 1930 s. What mass of copper is deposited? (Cu = 63.5, F = 96 500 C mol⁻¹)
- A. 0.159 g
- B. 0.0318 g
- C. 0.318 g
- D. 0.635 g
Q28. What is the main function of the salt bridge in a galvanic cell?
- A. To prevent the electrodes from reacting
- B. To supply electrons to the cathode
- C. To allow the two solutions to mix freely
- D. To complete the circuit and maintain electrical neutrality of the two solutions
Q29. Impure copper is purified by electrolysis in copper(II) sulphate solution using an impure copper anode and a pure copper cathode. What happens at the anode?
- A. Copper atoms are oxidised to Cu²⁺ and the anode dissolves
- B. Copper ions are reduced to copper metal
- C. Hydrogen gas is evolved
- D. Oxygen gas is evolved
Q30. While a lead–acid car battery is discharging, which change occurs?
- A. Lead dioxide forms at both electrodes
- B. The concentration of sulphuric acid increases
- C. Both electrodes become coated with PbSO₄ and the density of the acid falls
- D. Hydrogen gas is produced at the anode