OCR A-Level Chemistry AS Depth in chemistry (02), June 2018: Question 6

✅ Correct Answer

Steam ( H₂O(g) ) AND Acid / H⁺ catalyst (e.g., concentrated H₃PO₄ or H₂SO₄ ).

💡 Key Knowledge

Reaction 1 is an industrial hydration reaction used to convert alkenes into alcohols. Both reagents/conditions must be stated to secure the single mark.

❌ Common Errors

Writing "water" instead of "steam" (since industrial hydration uses gaseous water at high temperature and pressure). Omitting the catalyst description will also lose the mark.

✅ Correct Answer

1,2-dibromo-1,1-dichloroethane

🧠 Exam Technique

Number the longest carbon chain starting from the end that gives the lowest locant numbers for substituents. Remember to list substituents alphabetically ( bromo before chloro ), ignoring number prefixes like di-.

✅ Correct Answer

• 1st curly arrow: From the C=C double bond to the δ⁺ Br atom of the Br-Br bond.
• 2nd curly arrow: Representing heterolytic fission of the Br-Br bond, going from the bond to the δ⁻ Br atom, showing δ⁺ Br and δ⁻ Br dipoles correctly labeled.
• 3rd curly arrow: From the lone pair (or minus charge) on the resulting bromide ion ( :Br⁻ ) to the positively charged carbon ( C⁺ ) of the carbocation intermediate.

❌ Common Errors

Starting the first curly arrow from a carbon atom instead of the C=C bond. Failing to include intermediate partial charges ( δ⁺ / δ⁻ ) on the halogen molecule, or showing a partial charge on the carbocation carbon instead of a full + sign.

✅ Correct Answer

Equation showing n molecules of the monomer with a C=C double bond reacting to form the repeat unit enclosed in square brackets with an n subscript on the right, and 'side bonds' extending through the brackets.

🧠 Exam Technique

Ensure n is placed correctly: as a full-size coefficient on the reactant monomer on the LHS, and as a subscript outside the right-hand bracket on the RHS.

❌ Common Errors

Leaving the double bond in the polymer chain, forgetting the extending 'side bonds' passing through the brackets, or drawing skeletal/condensed structures instead of fully displayed formulae.

✅ Correct Answer

Advantage: Energy / electricity generation, or reduced use of fossil fuels.
Disadvantage: Formation of toxic gases like HCl / Cl₂ causing acid rain, or formation of greenhouse gases like CO₂ causing global warming.

💡 Key Knowledge

Because Compound C contains chlorine atoms, combustion produces acidic hydrogen chloride gas ( HCl ), which is a key environmental hazard distinct from standard hydrocarbon combustion.