OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), June 2022: Question 1

1 mark · Medium difficulty · Multiple Choice

Identify the remaining silver halide precipitates after adding silver nitrate followed by excess dilute ammonia to a mixture of chloride, bromide, and iodide ions.

Practise this question

Question

Multiple choice question 1 asking which compound(s) are present in the residue when an aqueous solution containing chloride, bromide, and iodide ions is treated with silver nitrate followed by excess dilute ammonia and filtered. Four options are given: A, AgCl only; B, AgCl and AgBr; C, AgBr only; D, AgBr and AgI. An empty answer box is at the bottom left and [1] is at the bottom right.
Question text

1 An aqueous solution contains a mixture of chloride, bromide and iodide ions.

AgNO3(aq) is added to this mixture, followed by an excess of dilute NH3(aq).

The resulting mixture is then filtered.

Which compound(s) is/are present in the residue on the filter paper?

A AgCl only

B AgCl and AgBr

C AgBr only

D AgBr and AgI

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme table showing question number 1, the correct answer D, 1 mark, and AO element 2.7.

AO

Question Answer Marks Guidance

element

1 D 1 2.7

How to answer it

Halide Precipitates and Ammonia Solubility

What this question tests

This question assesses your knowledge of qualitative analysis, specifically testing your understanding of silver halide precipitation reactions with silver nitrate ( AgNO₃ ) followed by the differential solubility of silver chloride, silver bromide, and silver iodide precipitates in dilute aqueous ammonia ( NH₃ ).

Question 1

Correct Answer: D

✅ Correct Answer

D: AgBr and AgI

When AgNO₃(aq) is added to a mixture containing Cl⁻ , Br⁻ , and I⁻ ions, white, cream, and yellow precipitates of AgCl , AgBr , and AgI are formed respectively. Upon adding an excess of dilute NH₃(aq) , the silver chloride precipitate ( AgCl ) dissolves completely, leaving AgBr and AgI remaining as the solid residue on the filter paper.

💡 Key Knowledge

  • AgCl : White precipitate, readily soluble in dilute NH₃(aq) .
  • AgBr : Cream precipitate, insoluble in dilute NH₃(aq) but soluble in concentrated NH₃(aq) .
  • AgI : Yellow precipitate, insoluble in both dilute and concentrated NH₃(aq) .

🧠 Exam Technique

Read multiple-choice questions carefully to check whether dilute or concentrated ammonia is specified. Examiners frequently use dilute ammonia to test if you know that silver chloride dissolves while silver bromide does not.

❌ Common Errors

  • Assuming all silver halides dissolve in dilute ammonia.
  • Confusing the solubility rules for AgBr and AgCl . Remember: AgBr requires concentrated ammonia to dissolve.
  • Forgetting that AgI is insoluble in all strengths of ammonia due to its extremely low solubility product.
Mark Allocation: [1] mark awarded for selecting option D.

Topics

Module 3: Periodic table and energy · Practical Activity Groups · 3.1 The periodic table · PAG 4: Qualitative analysis of ions

Question and mark scheme from the OCR A-Level Chemistry examination, Periodic table, elements and physical chemistry (01), June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.