OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2024: Question 3

1 mark · Easy difficulty · Multiple Choice

Identify the colour of the precipitate formed when iodoalkanes react with aqueous silver nitrate in ethanol.

Practise this question

Question

Multiple choice question 3 asks for the colour of precipitate seen when investigating the rate of hydrolysis of different iodoalkanes using aqueous silver nitrate in ethanol. Four options are given: A Brown, B Cream, C White, D Yellow, alongside an answer box and mark allocation of [1].
Question text

3 A student investigates the rate of hydrolysis of different iodoalkanes using aqueous silver nitrate

in ethanol.

What colour of precipitate is seen?

A Brown

B Cream

C White

D Yellow

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 3 is D, worth 1 mark.

3 D 1

How to answer it

Hydrolysis of Iodoalkanes: Precipitate Colours

What this question tests

This question assesses your factual recall of halide precipitate colours formed during the halogenoalkane hydrolysis practical using aqueous silver nitrate. You need to link the specific halogen present in the iodoalkane (iodine/iodide ions) to the correct silver halide precipitate colour.

Question 3

Identifying the Halide Precipitate

✅ Correct Answer: D (Yellow)

When an iodoalkane undergoes hydrolysis in the presence of aqueous silver nitrate, iodide ions (I⁻) are released into solution. These react with silver ions (Ag⁺) to form a yellow precipitate of silver iodide ( AgI ).

💡 Key Knowledge: Silver Halide Colours

  • Chloride (Cl⁻): White precipitate ( AgCl )
  • Bromide (Br⁻): Cream precipitate ( AgBr )
  • Iodide (I⁻): Yellow precipitate ( AgI )

🧠 Exam Technique

Multiple choice questions involving practical observations often test colour changes or precipitates. Eliminate distractors systematically: white is for chloride, cream is for bromide, and yellow is for iodide. Ensure you do not confuse the organic reagents with the resulting inorganic precipitates.

❌ Common Errors

Students occasionally confuse silver halide colours with flame test colours or transition metal complex colours. Another common mistake is guessing "cream" (associated with bromine) due to hesitation over the exact shade of silver iodide.

Mark Allocation: 1 mark for selecting D.

Topics

Module 4: Core organic chemistry · Practical Activity Groups · PAG 7: Qualitative analysis of organic functional groups · 4.2 Alcohols, haloalkanes and analysis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.