NUMS — Medical & Dental Entry Test

NUMS Chemistry — Kinetics, Acids and Bases, Electrochemistry (Set 1)

Take the NUMS Chemistry — Kinetics, Acids and Bases, Electrochemistry (Set 1): 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. A reaction follows the rate law: rate = k[A]²[B]. If the concentrations of both A and B are doubled, the rate becomes:
- A. 2 times
- B. 8 times ✓
- C. 4 times
- D. 6 times
Answer: B. 8 times
Explanation: New rate = k(2[A])²(2[B]) = 4 × 2 = 8 times the original rate.
Q2. Radioactive decay and many drug-elimination processes are first order. In what units is the rate constant of such a process expressed (time in seconds)?
- A. mol⁻¹ s
- B. s⁻¹ ✓
- C. mol dm⁻³ s⁻¹
- D. dm³ mol⁻¹ s⁻¹
Answer: B. s⁻¹
Explanation: For first order, rate = k[A], so k = rate/[A] = (mol dm⁻³ s⁻¹)/(mol dm⁻³) = s⁻¹.
Q3. A drug is eliminated from plasma by first-order kinetics with a half-life of 4 hours. What percentage of the initial dose remains in the plasma after 12 hours?
- A. 6.25%
- B. 25%
- C. 33.3%
- D. 12.5% ✓
Answer: D. 12.5%
Explanation: 12 h = 3 half-lives; fraction left = (½)³ = 1/8 = 12.5%.
Q4. A first-order decomposition has a rate constant of 0.0231 min⁻¹. What is its half-life?
- A. 30 min ✓
- B. 43 min
- C. 15 min
- D. 3.0 min
Answer: A. 30 min
Explanation: t½ = 0.693/k = 0.693/0.0231 = 30 min.
Q5. Alcohol is removed from the blood by the liver at a nearly constant rate (about the same number of grams per hour) whatever its concentration. This elimination is best described as:
- A. First order
- B. Pseudo-first order
- C. Zero order ✓
- D. Second order
Answer: C. Zero order
Explanation: A rate independent of concentration (rate = k) is the definition of a zero-order process; the enzyme is saturated.

The other 25 questions

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Q6. Enzymes such as catalase speed up biochemical reactions enormously. How do they do this?
- A. By shifting the equilibrium towards products
- B. By providing a pathway of lower activation energy
- C. By increasing the temperature of the cell
- D. By increasing the enthalpy change of the reaction
Q7. A rough rule says the rate of many reactions doubles for every 10 °C rise in temperature. By what factor would the rate increase if the temperature rose from 20 °C to 50 °C?
- A. 8
- B. 30
- C. 6
- D. 3
Q8. According to the Arrhenius equation k = A e^(−Eₐ/RT), a graph of ln k against 1/T is a straight line. What is its slope?
- A. −Eₐ/R
- B. −Eₐ/RT
- C. +Eₐ/R
- D. ln A
Q9. Which statement about order and molecularity is correct?
- A. Order can be predicted from the balanced equation alone
- B. Order is found experimentally and can be fractional; molecularity is always a whole number
- C. Molecularity can be zero or fractional, while order is always whole
- D. Order and molecularity are always equal
Q10. In a multi-step reaction mechanism, the overall rate is controlled by:
- A. The first step always
- B. The fastest step
- C. The last step always
- D. The slowest step
Q11. Gastric juice can be modelled as 0.01 M HCl. What is its pH?
- A. 2
- B. 12
- C. 1
- D. 0.01
Q12. What is the pH of a 0.001 M NaOH solution at 25 °C?
- A. 11
- B. 3
- C. 13
- D. 10
Q13. Normal arterial blood has a pH of 7.4. What is the hydrogen ion concentration in blood?
- A. 4.0 × 10⁻⁸ M
- B. 7.4 × 10⁻⁸ M
- C. 2.5 × 10⁻⁷ M
- D. 1.0 × 10⁻⁷ M
Q14. Blood is buffered mainly by H₂CO₃/HCO₃⁻ (pKa = 6.1). If the ratio [HCO₃⁻]/[H₂CO₃] in plasma is 20 : 1, what is the pH of the blood?
- A. 8.1
- B. 7.4
- C. 7.1
- D. 6.1
Q15. A buffer is prepared with equal concentrations of ethanoic acid (pKa = 4.74) and sodium ethanoate. What is its pH?
- A. 9.26
- B. 2.37
- C. 4.74
- D. 7.00
Q16. Phosphate buffers are important inside cells. What is the conjugate base of H₂PO₄⁻?
- A. H₃PO₄
- B. PO₄³⁻
- C. HPO₄²⁻
- D. H₂PO₄²⁻
Q17. Which species acts as a Lewis acid?
- A. NH₃
- B. H₂O
- C. BF₃
- D. Cl⁻
Q18. What is the approximate pH of 0.1 M ethanoic acid? (Ka = 1.8 × 10⁻⁵)
- A. 4.74
- B. 3.87
- C. 2.87
- D. 1.00
Q19. Which salt gives a basic solution when dissolved in water?
- A. NH₄Cl
- B. Na₂CO₃
- C. KNO₃
- D. NaCl
Q20. At 37 °C (body temperature), Kw is larger than 1.0 × 10⁻¹⁴. Which statement about pure water at 37 °C is correct?
- A. Its pH is above 7 and it is basic
- B. Its pH is below 7 and it is acidic
- C. Its pH is below 7, but it is still neutral
- D. Its pH is exactly 7
Q21. Among the four oxyacids of chlorine listed, which one ionises most completely in water?
- A. HClO₃
- B. HClO₄
- C. HClO
- D. HClO₂
Q22. A student titrates vinegar (ethanoic acid) against standard NaOH solution. Which indicator should be chosen so that its colour change matches the equivalence point?
- A. Litmus
- B. Methyl orange
- C. Methyl red
- D. Phenolphthalein
Q23. What volume of 0.05 M NaOH is needed to neutralise 25 cm³ of 0.1 M HCl?
- A. 12.5 cm³
- B. 100 cm³
- C. 25 cm³
- D. 50 cm³
Q24. Potassium dichromate, K₂Cr₂O₇, is used in breathalysers. What is the oxidation number of chromium in this compound?
- A. +12
- B. +6
- C. +3
- D. +7
Q25. A galvanic cell is built from Ni²⁺/Ni (E° = −0.25 V) and Ag⁺/Ag (E° = +0.80 V) half-cells. What is its standard emf?
- A. 1.85 V
- B. 0.55 V
- C. 1.05 V
- D. 1.35 V
Q26. A zinc–copper Daniell cell is powering a small bulb. Which statement about the electrodes of this cell is correct?
- A. Electrons flow from copper to zinc through the salt bridge
- B. Zinc is oxidised at the anode, which is the negative electrode
- C. Copper is oxidised at the cathode, which is negative
- D. Zinc is reduced at the anode, which is positive
Q27. A charge of 9650 C is passed through silver nitrate solution. What mass of silver is deposited at the cathode? (Ag = 108, F = 96500 C mol⁻¹)
- A. 1.08 g
- B. 21.6 g
- C. 10.8 g
- D. 108 g
Q28. When brine (concentrated aqueous NaCl) is electrolysed with inert electrodes, which product forms at the cathode?
- A. Oxygen gas
- B. Chlorine gas
- C. Sodium metal
- D. Hydrogen gas
Q29. Which metal cannot liberate hydrogen gas from dilute hydrochloric acid?
- A. Copper
- B. Magnesium
- C. Zinc
- D. Iron
Q30. In the titration of iron(II) tablets with purple potassium permanganate in acid, the manganese ends up as colourless Mn²⁺. How many electrons are gained per manganese atom?
- A. 5
- B. 2
- C. 3
- D. 7