OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2017: Question 5

1 mark · Easy difficulty · Multiple Choice

Identify which type of reaction has the greatest atom economy among substitution, hydrolysis, elimination, and addition.

Practise this question

Question

Multiple choice question 5 asks 'Which type of reaction has the greatest atom economy?' with four options: A Substitution, B Hydrolysis, C Elimination, and D Addition. An empty box is provided for 'Your answer', with [1] mark indicated on the bottom right.
Question text

5 Which type of reaction has the greatest atom economy?

A Substitution

B Hydrolysis

C Elimination

D Addition

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme shows question number 5 with the correct answer D and 1 mark awarded.

5 D 1

How to answer it

Exam Question Study Guide: Atom Economy

OCR A-Level Chemistry • Multiple Choice

What this question tests

This question assesses your understanding of atom economy and how it relates to different fundamental types of organic and inorganic reactions (substitution, hydrolysis, elimination, and addition). You must know how products are formed in each reaction type to determine which pathway converts 100% of reactant atoms into the desired product.

Question 5: Types of Reaction & Atom Economy

Which type of reaction has the greatest atom economy?

A Substitution
B Hydrolysis
C Elimination
D Addition

✅ Correct Answer

D (Addition)

Addition reactions involve two or more reactants combining to form a single product, resulting in no waste by-products and an atom economy of exactly 100%.

💡 Key Knowledge

  • Atom Economy Formula: (Mass of desired product / Total mass of reactants) × 100
  • Addition: Reactants → 1 Product (100% atom economy).
  • Substitution / Hydrolysis / Elimination: Produce two or more products, meaning some atoms form unwanted by-products (lower atom economy).

🧠 Exam Technique

For multiple-choice questions involving definitions or general principles, mentally write out a generic balanced equation for each option. Ask yourself: "Does this reaction produce a by-product like H₂O, HCl, or small molecules alongside the main product?" If the answer is no, it has the maximum atom economy.

❌ Common Errors

Students sometimes confuse percentage yield with atom economy. While yield depends on practical losses and side reactions, atom economy is a theoretical value calculated purely from the stoichiometry of the balanced chemical equation.

Mark Breakdown: 1 mark available for selecting option D.

Topics

Module 2: Foundations in chemistry · Module 4: Core organic chemistry · 2.1 Atoms and reactions · 4.1 Basic concepts and hydrocarbons

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2017. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.