OCR A-Level Chemistry AS Breadth in chemistry (01), November 2020: Question 4

1 mark · Easy difficulty · Multiple Choice

Identify which Group 2 compound would not be suitable to neutralise acid soils or treat acid indigestion from a given multiple-choice list.

Practise this question

Question

Multiple choice question 4 asking which Group 2 compound would not be suitable for neutralising acid soils or treating acid indigestion, with options A (BaSO4), B (CaCO3), C (Ca(OH)2), and D (Mg(OH)2), alongside an answer box and mark allocation of [1].
Question text

4 Some Group 2 compounds can be used to neutralise acid soils and to treat acid indigestion.

Which Group 2 compound would not be suitable for either use?

A BaSO4

B CaCO3

C Ca(OH)2

D Mg(OH)2

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer for question 4 is A, worth 1 mark.

4 A 1 1.1

How to answer it

Group 2 Compounds and Neutralisation

What this question tests

This question assesses your knowledge of Group 2 chemistry, specifically the solubility trends of Group 2 sulfates and hydroxides/carbonates, and the practical applications of basic compounds in neutralising acids (such as in agriculture and medicine).

Question 4

Identifying Unsuitable Neutralising Agents

✅ Correct Answer

A: BaSO₄

Barium sulfate is completely insoluble in water and acids. Therefore, it cannot react with or neutralise excess acid in soils or the stomach.

💡 Key Knowledge

  • Group 2 Sulfates: Solubility decreases down the group (MgSO₄ is soluble, BaSO₄ is insoluble).
  • Neutralisation Requirements: To neutralise an acid effectively, a compound must either dissolve to release OH⁻ ions or react as a base (like carbonates). Insoluble solids like BaSO₄ cannot act efficiently.
  • Alternative uses: Barium sulfate is safely used in medicine as a "barium meal" for X-rays precisely because it is insoluble and toxic if dissolved.

🧠 Exam Technique

Read multiple-choice stems carefully for negative qualifiers like not . Eliminate options that you know are correct uses: CaCO₃ (limestone) and Ca(OH)₂ (slaked lime) are standard agricultural treatments, while Mg(OH)₂ ("milk of magnesia") treats indigestion.

❌ Common Errors

Students often confuse the solubility trends of Group 2 sulfates with Group 2 hydroxides. Remember: sulfates get less soluble down the group, whereas hydroxides get more soluble down the group.

Mark Allocation: [1] mark for selecting option A.

Topics

Module 3: Periodic table and energy · 3.1 The periodic table

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.