IB Diploma Chemistry chapter 6: Reactivity 3: What are the mechanisms of chemical change? MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

42 exam-style questions on Reactivity 3: What are the mechanisms of chemical change?, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

42 questions · 4 topics · 10 per test

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What chapter 6 covers

Ten Reactivity 3: What are the mechanisms of chemical change? questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. What is a radical?

  1. A
    a species with an unpaired electron
  2. B
    a positively charged ion
  3. C
    a species with a lone pair that it can donate
  4. D
    an atom with a full outer shell
Show answer

Answer: A. A radical has an unpaired electron (shown as a dot), which makes it very reactive.

2. Which change is a reduction?

  1. A
    Fe2+ → Fe3+
  2. B
    Cl− → Cl2
  3. C
    MnO4− → Mn2+
  4. D
    SO2 → SO42−
Show answer

Answer: C. Mn goes from +7 to +2: a decrease in oxidation state is reduction. The other three are increases (+2 to +3, −1 to 0, +4 to +6).

3. Why are radicals very reactive?

  1. A
    they carry a positive charge
  2. B
    they have full outer shells
  3. C
    they are always ions
  4. D
    they have an unpaired electron that readily pairs up by forming a new bond
Show answer

Answer: D. The unpaired electron makes a radical seek another electron to form a covalent bond. Radicals are usually neutral, not ions.

4. What is a Brønsted–Lowry acid?

  1. A
    a proton acceptor
  2. B
    a substance that produces OH− ions in water
  3. C
    an electron-pair acceptor
  4. D
    a proton donor
Show answer

Answer: D. Brønsted–Lowry acids donate H+ (protons) and bases accept them. An electron-pair acceptor is the Lewis definition.

5. Ethene reacts with hydrogen bromide. What is the product?

  1. A
    1,2-dibromoethane
  2. B
    bromoethene
  3. C
    ethanol
  4. D
    bromoethane
Show answer

Answer: D. HBr adds across the C=C bond: CH2=CH2 + HBr → CH3CH2Br. 1,2-dibromoethane forms with Br2.

6. What is the pH of 0.0010 mol dm−3 hydrochloric acid?

  1. A
    1.0
  2. B
    11.0
  3. C
    3.0
  4. D
    −3.0
Show answer

Answer: C. HCl is a strong acid, so [H+] = 1.0 × 10−3 mol dm−3 and pH = −log(1.0 × 10−3) = 3.0. The minus sign in the definition makes pH positive here.

7. In the reaction of 1-chloropropane with hydroxide ions, what is the leaving group?

  1. A
    OH−
  2. B
    H+
  3. C
    Cl−
  4. D
    Na+
Show answer

Answer: C. The chlorine leaves with both electrons of the C–Cl bond, as Cl−. OH− is the nucleophile that takes its place.

8. 20.0 cm3 of 0.100 mol dm−3 HCl is mixed with 10.0 cm3 of 0.100 mol dm−3 NaOH. What is the pH of the mixture?

  1. A
    3.0
  2. B
    1.5
  3. C
    1.3
  4. D
    7.0
Show answer

Answer: B. H+ 2.00 × 10−3 mol minus OH− 1.00 × 10−3 mol leaves 1.00 × 10−3 mol H+ in 30.0 cm3: [H+] = 0.0333 mol dm−3, pH = 1.5. Ignoring the added volume gives 1.3.

9. Pentane, CH3CH2CH2CH2CH3, reacts with chlorine in UV light. How many different structural isomers of C5H11Cl can form?

  1. A
    2
  2. B
    3
  3. C
    5
  4. D
    12
Show answer

Answer: B. By symmetry, carbons 1 and 5 are equivalent, as are 2 and 4, so the products are 1-, 2- and 3-chloropentane. Counting every carbon (5) or every H atom (12) ignores the symmetry.

10. Which species is amphiprotic?

  1. A
    HCO3−
  2. B
    CO32−
  3. C
    NH4+
  4. D
    Cl−
Show answer

Answer: A. HCO3− can donate H+ (forming CO32−) or accept H+ (forming H2CO3). CO32− can only accept; NH4+ can only donate.

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Reactivity 3: What are the mechanisms of chemical change?: questions students ask

How many Reactivity 3: What are the mechanisms of chemical change? MCQs are there?

42, each with the answer and a short explanation, across 4 topics: R3.1 Proton transfer reactions, R3.2 Electron transfer reactions, R3.3 Electron sharing reactions, R3.4 Electron-pair sharing reactions. Every chapter test draws ten of them, so you can take it many times.

Is the IB Diploma Chemistry chapter 6 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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