OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2018: Question 14

1 mark · Medium difficulty · Multiple Choice

Identify the true statements regarding the purification of a solid organic compound by recrystallisation.

Practise this question

Question

Multiple-choice question 14 asks which statements about the purification of a solid organic compound by recrystallisation are true, given three numbered statements: 1. The organic compound is more soluble in hot solvent, 2. The hot solution is cooled before the purified organic compound is collected, and 3. The melting point of the purified organic compound is lower than the impure compound. Four options A (1, 2 and 3), B (Only 1 and 2), C (Only 2 and 3), and D (Only 1) are provided along with an answer box.
Question text

14 A solid organic compound can be purified by recrystallisation.

Which statement(s) about recrystallisation is/are true?

1 The organic compound is more soluble in hot solvent.

2 The hot solution is cooled before the purified organic compound is collected.

3 The melting point of the purified organic compound is lower than the impure compound.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme table indicates that the correct answer for question 14 is B, worth 1 mark.

14 B 1

How to answer it

Recrystallisation Principles and Melting Point Purity

What this question tests

This question assesses your practical knowledge of purification techniques in organic chemistry, specifically recrystallisation, and your understanding of how impurities affect the physical properties (such as melting point) of organic solids.

Question 14: Multiple Choice Analysis

Evaluating Statements on Recrystallisation and Melting Point

✅ Correct Answer: Option B (Only 1 and 2)

Statement 1 and Statement 2 are scientifically correct descriptions of a successful recrystallisation procedure. Statement 3 contains a classic inversion error regarding melting points.

💡 Key Knowledge: Statement 1 & 2

  • Statement 1 (True): Organic compounds must be dissolved in a minimum volume of hot solvent so that a concentrated solution is formed, allowing maximum crystallisation upon cooling.
  • Statement 2 (True): The hot solution must be allowed to cool down so that crystals of the purified product precipitate out of solution while soluble impurities remain dissolved.

❌ Common Errors: Statement 3

Statement 3 is FALSE. Impurities actually lower the melting point and cause the melting range to broaden. Therefore, a pure organic compound has a higher and sharper melting point than an impure one.

🧠 Exam Technique

In "Which statement(s) are true" multiple-choice questions, evaluate each statement independently. Cross out options as you eliminate false statements (like Statement 3) to quickly narrow down to the correct combination.

Mark Allocation: [1 mark] awarded for selecting B.

Topics

Module 4: Core organic chemistry · Practical Activity Groups · 4.2 Alcohols, haloalkanes and analysis · PAG 6: Synthesis of an organic solid

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.