This exam focus covers Exam Focus within Acids and Alkalis for GCSE Chemistry. Revise Acids and Alkalis in Chemical Changes for GCSE Chemistry with 25 exam-style questions and 21 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 10 of 12 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
🎯 Exam Focus
Frequently Examined
Acids and alkalis underpin much of Unit 4. Common question types include:
- Identify the ion: "Name the ion responsible for the acidity of hydrochloric acid" — always H⁺ (1 mark)
- Indicator colours: "What colour would universal indicator turn in sodium hydroxide solution?" (1-2 marks)
- Equations: Write the equation for an acid releasing H⁺ ions in water (1-2 marks)
- Higher Tier: Explain the difference between a strong and weak acid, or between concentrated and dilute (3 marks)
- Practical questions: How to measure the pH of a solution and what the reading tells you (2-3 marks)
Key phrase examiners love: "The ion responsible for acidity is H⁺ (hydrogen ions)." Learn this as a one-line answer.
Edexcel 1CH0: Examined in Paper 1 (1CH0/1). Core Practical CP4 (investigating the change in pH when a strong acid neutralises a strong alkali) is directly examined — expect questions on method, safety, and interpreting pH readings. In Edexcel-style questions, the command word "Suggest" appears frequently — use your chemistry knowledge to apply to an unfamiliar context.
Quick Check: A student says "concentrated ethanoic acid is a strong acid." What two errors has the student made?
1) Concentrated does not mean strong — concentration is about how much acid is dissolved per unit volume, while strength is about how much the acid ionises in water. 2) Ethanoic acid is a WEAK acid — it only partially ionises in water (CH₃COOH ⇌ H⁺ + CH₃COO⁻). It can be concentrated OR dilute, but it is always a weak acid.
Quick Check: Name the ion responsible for making a solution acidic, and the ion responsible for making it alkaline.
Acidic: H⁺ (hydrogen ions). Alkaline: OH⁻ (hydroxide ions). These are the defining ions for acidity and alkalinity respectively.
Quick Check: What colour does litmus paper turn in a solution of hydrochloric acid, and what does this indicate about its pH?
Litmus paper turns red in hydrochloric acid. This indicates the solution is acidic — pH below 7. HCl releases H⁺ ions in water.
Practice questions for Acids and Alkalis
Which ion do acids produce when dissolved in water?
Explain the difference between a strong acid and a concentrated acid.