OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), June 2019: Question 9

1 mark · Medium difficulty · Multiple Choice

Identify which statement is not correct for Group 2 hydroxides among the given options.

Practise this question

Question

Multiple choice question 9 asking which statement is not correct for Group 2 hydroxides, with four options A to D: A states Mg(OH)2 can be used to treat indigestion, B states Ca(OH)2 is used in agriculture to neutralise alkaline soils, C states the anion in Sr(OH)2 contains 10 electrons, and D states Ba(OH)2 is a product from the reaction of barium and water.
Question text

9 Which statement is not correct for Group 2 hydroxides?

A Mg(OH)2 can be used to treat indigestion.

B Ca(OH)2 is used in agriculture to neutralise alkaline soils.

C The anion in Sr(OH)2 contains 10 electrons.

D Ba(OH)2 is a product from the reaction of barium and water.

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme for question 9 showing the correct answer as B, worth 1 mark.

9 B 1 AO1.1

How to answer it

Properties and Uses of Group 2 Hydroxides

What this question tests

This question assesses your factual recall and understanding of Group 2 chemistry (alkaline earth metals), specifically focusing on the practical uses of their hydroxides, their acid-base properties in agriculture, atomic structure of ions (electron counting), and their reactions with water.

Question 9 Analysis

Identifying the Incorrect Statement

✅ Correct Answer: Option B

Ca(OH)₂ is used to neutralise acidic soils, not alkaline soils. Therefore, statement B is factually incorrect and is the correct choice.

💡 Key Knowledge: Statement Breakdown

  • A: Mg(OH)₂ (milk of magnesia) is weakly alkaline and safely neutralises excess stomach acid (indigestion). This is correct.
  • C: The anion is hydroxide ( OH⁻ ). Oxygen has 8 electrons, hydrogen has 1, and the negative charge adds 1 more (8 + 1 + 1 = 10 electrons). This is correct.
  • D: Barium reacts vigorously with water to form barium hydroxide and hydrogen gas ( Ba + 2H₂O → Ba(OH)₂ + H₂ ). This is correct.

🧠 Exam Technique

Read multiple-choice stems extremely carefully, especially words printed in bold like not. Many students lose easy marks here by looking for the first true statement and selecting it immediately.

❌ Common Errors

Students frequently confuse the agricultural use of calcium hydroxide ( Ca(OH)₂ , slaked lime). Because soils become acidic due to acid rain and decaying matter, farmers add lime to raise the pH, meaning it neutralises acid—not alkali.

Mark Scheme Allocation: 1 mark awarded for selecting B. (AO1.1 - Demonstrate knowledge and understanding of scientific ideas).

Topics

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

Question and mark scheme from the OCR A-Level Chemistry examination, Periodic table, elements and physical chemistry (01), June 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.