OCR A-Level Chemistry AS Breadth in chemistry (01), June 2022: Question 3

1 mark · Easy difficulty · Multiple Choice

Identify which of the given compounds is an alkali

Practise this question

Question

Multiple choice question asking which compound is an alkali, with four options: A, CH3COOH; B, CH3OH; C, HNO3; D, NH3. There is an answer box labelled 'Your answer' and a mark allocation of [1] on the bottom right.
Question text

3 Which compound is an alkali?

A CH3COOH

B CH3OH

C HNO3

D NH3

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer for question 3 is option D, worth 1 mark under assessment objective AO1.1.

3 D 1 AO1.1

How to answer it

Identifying an Alkali

What this question tests

This question assesses your foundational understanding of acid-base definitions at AS Level (AO1.1). Specifically, it tests your ability to distinguish between acids, neutral molecular compounds, and alkalis (soluble bases that release hydroxide ions or accept protons in aqueous solution).

Question 3

Multiple Choice Part

Which compound is an alkali?

✅ Correct Answer: D ( NH₃ )

Ammonia is a weak base that dissolves in water to form an alkaline solution. It accepts a proton from water molecules according to the equation:

NH₃ (aq) + H₂O (l) ⇌ NH₄⁺ (aq) + OH⁻ (aq)

Because it produces hydroxide ions ( OH⁻ ) in aqueous solution, it qualifies as an alkali.

💡 Key Knowledge

  • Base vs Alkali: An alkali is a soluble base that releases hydroxide ions ( OH⁻ ) in aqueous solution.
  • CH₃COOH (Option A) is ethanoic acid (a weak carboxylic acid).
  • CH₃OH (Option B) is methanol (a neutral alcohol).
  • HNO₃ (Option C) is nitric acid (a strong mineral acid).

🧠 Exam Technique

Go through the options systematically and classify each chemical family:

  • Spot functional groups: -COOH means acid, -OH on a hydrocarbon chain usually means alcohol/neutral.
  • Recall common strong acids ( HNO₃ , HCl , H₂SO₄ ) to quickly rule them out.
  • Remember that ammonia ( NH₃ ) is a classic example of a gaseous base that forms an alkaline solution.

❌ Common Errors

  • Mistaking methanol ( CH₃OH ) for an alkali simply because it contains an -OH group. Alcohols do not ionise to release OH⁻ ions in water.
  • Forgetting that ammonia acts as a base/alkali despite not having a metal hydroxide formula like NaOH .
Mark breakdown: 1 mark available for selecting option D.

Topics

Module 2: Foundations in chemistry · 2.1 Atoms and reactions

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