Grade 12 Physical Sciences · Matter and Materials

Write addition reactions and conditions

Write addition reactions where atoms are added across a double bond, and give their conditions (ethene + H₂O → ethanol).

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Addition reactions Organic Chemistry ReactionsMiss Martins Maths and Science

Reactions Organic Chemistry Grade 12 | Alkene - AlcoholKevinmathscience

Organic Chemistry Reactions Addition vs Substitution vs Elimination: How to identifyMiss Martins Maths and Science

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Question 1.2 · November 2025 · Paper 2 · National (DBE) · 2 marks

Various options are provided as possible answers to the following questions. Each question has only ONE correct answer.

1.2 The organic compound

C_{2} H_{4}

is converted to an alkane as shown by the reaction below.

C_{2} H_{4} \to

Alkane

Which ONE of the following is a suitable catalyst for this reaction?(2)

A Lead
B Platinum
C Hydrogen
D Iron

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More past paper questions: write addition reactions and conditions

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3. Question 4.2.4 · November 2025 · Paper 2 · National (DBE) · 3 marks
4.2 A compound with the formula $C_{10} H_{22}$ undergoes a cracking reaction according to the equation:

$C_{10} H_{22} (ℓ) \to 2 X(g) + C_{4} H_{10} (g)$

The mixture of the two products is bubbled in bromine water, $Br_{2}$ (aq), in a darkened room.

Answer the questions that follow.
4.2.4 Which compound, X or $C_{4} H_{10}$ , reacts faster with $Br_{2}$ (aq)? Explain the answer.(3)
Show the memo (3 ticks)Memo
1. ✓
  ChoiceX / $C_{3} H_{6}$ / Propene
  1 mark · Write addition reactions and conditions
2. ✓
  X is unsaturatedX is unsaturated / has a double bond / is an alkene.
  1 mark · Write addition reactions and conditions
3. ✓
  X undergoes additionX undergoes addition.
  ANY ONE OR: Alkenes are more reactive than alkanes / Unsaturated compounds react faster than saturated compounds. Addition reaction is faster than substitution. Addition reaction does not need UV/light.
  1 mark · Write addition reactions and conditions
4. Question 1.3 · November 2022 · Paper 2 · National (DBE) · 2 marks
Various options are provided as possible answers to the following questions. Each question has only ONE correct answer.
1.3 A test tube contains a liquid hydrocarbon.

When bromine water ( $Br_{2}$ ) is added to the test tube, the mixture decolourises IMMEDIATELY.

Which ONE of the following combinations correctly identifies the COMPOUND and the TYPE OF REACTION that takes place in the test tube?(2)
1. A Compound: hexane; type of reaction: addition
2. B Compound: hexane; type of reaction: substitution
3. C Compound: hex-2-ene; type of reaction: addition
4. D Compound: hex-2-ene; type of reaction: substitution
Show the memo (1 tick)Memo
1. ✓
  Correct optionImmediate decolourisation of bromine water shows an unsaturated compound: the $Br_{2}$ adds across the C=C double bond of hex-2-ene (halogenation, an addition reaction). Hexane (saturated) reacts with bromine only slowly by substitution, in light.
  
  Answer: C
  2 marks · Write addition reactions and conditions
5. Question 1.2 · May/June 2022 · Paper 2 · National (DBE) · 2 marks
1.2 When $CH_{2} = CH_{2}$ is converted to $CH_{3} CH_{3}$ , the type of reaction is ...(2)
1. A hydration.
2. B hydrolysis.
3. C halogenation.
4. D hydrogenation.
Show the memo (1 tick)Memo
1. ✓
  Adding H2 across a double bond is hydrogenationEthene becomes ethane: two H atoms are added across the double bond ( $CH_{2} = CH_{2} + H_{2} \to CH_{3} CH_{3}$ ). Adding $H_{2}$ is hydrogenation. Hydration would add $H_{2} O$ and give an alcohol.
  
  Answer: D
  2 marks · Write addition reactions and conditions
6. Question 4.3.1 · May/June 2025 · Paper 2 · National (DBE) · 4 marks
In the flow diagram below, a primary alcohol P is used as a starting reactant to form different organic compounds under different reaction conditions.
4.3 Consider reaction III.

Write down:
4.3.1 The balanced equation using CONDENSED structural formulae(4)
Show the memo (4 ticks)Memo
1. ✓
  Alkene correct $CH_{2} CHCH_{2} CH_{3}$ (or $CH_{2} = CHCH_{2} CH_{3}$ )
  1 mark · Write addition reactions and conditions
2. ✓
  H2O $+ H_{2} O \to$
  1 mark · Write addition reactions and conditions
3. ✓
  Hydroxyl groupOH in the product
  1 mark · Write addition reactions and conditions
4. ✓
  Whole alcohol correct (OH on second C atom) $CH_{2} CHCH_{2} CH_{3} + H_{2} O \to CH_{3} CHOHCH_{2} CH_{3}$
  OR
  $CH_{2} = CHCH_{2} CH_{3} + H_{2} O \to CH_{3} CH(OH)CH_{2} CH_{3}$
  1 mark · Draw structural formulae

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