Cambridge IGCSE Chemistry 0620 · C7.1

Acids, Bases & Salts

A premium guided lesson covering characteristic reactions, indicators, pH, neutralisation, proton transfer, and strong versus weak acids. Designed for direct classroom teaching, student completion, revision, and exam preparation.

60–75 minutes Core + Supplement Manual-marking practice

Student information

Complete before starting the lesson.

MSH Premium

Learning objectives & success criteria

Students should be able to explain, predict, and apply acid-base reactions.

By the end of the lesson, I can...

  • Describe acid reactions with metals, bases, and carbonates.
  • Describe base reactions with acids and ammonium salts.
  • Use indicator colours to identify acidic, neutral, and alkaline solutions.
  • Write the ionic equation for neutralisation: H⁺ + OH⁻ → H₂O.
  • Compare strong and weak acids using degree of dissociation.

Exam success criteria

  • I use correct products: salt + hydrogen, salt + water, or salt + water + carbon dioxide.
  • I distinguish a base from an alkali: alkalis are soluble bases.
  • I explain strong acid as fully dissociated and weak acid as partially dissociated.
  • I avoid saying “strong acid is concentrated” unless concentration is actually being discussed.

Core teaching notes

Teacher-led explanation with clear equations and exam wording.

Core

Acid reactions

Acid + metalsalt + hydrogen gas · test: squeaky pop with a lit splint
Acid + basesalt + water · this is neutralisation
Acid + carbonatesalt + water + carbon dioxide · test: limewater turns milky

Base and alkali reactions

Base + acidsalt + water
Alkali + ammonium saltsalt + ammonia + water · ammonia turns damp red litmus blue
AlkaliA soluble base. Examples: sodium hydroxide, potassium hydroxide, aqueous ammonia.

Neutralisation equation

In every aqueous acid-alkali neutralisation, hydrogen ions react with hydroxide ions to form water:

H⁺(aq) + OH⁻(aq) → H₂O(l)

Indicators and pH

Use colour changes to classify solutions and compare acidity/alkalinity.

Core

Litmus

Acid: red
Alkali: blue

Thymolphthalein

Acid: colourless
Alkali: blue

Methyl orange

Acid: red
Alkali: yellow

Universal indicator pH scale

pH 0–6: acidic · pH 7: neutral · pH 8–14: alkaline.

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14

Supplement: proton transfer and acid strength

Useful for extended-response questions and higher-level explanations.

Supplement

Acid

An acid is a proton donor. It donates H⁺ ions in aqueous solution.

Base

A base is a proton acceptor. It accepts H⁺ ions during a reaction.

Strong vs weak

Strong acids fully dissociate. Weak acids partially dissociate.

Strong acid example

HCl → H⁺ + Cl⁻

Hydrochloric acid is fully dissociated in water.

Weak acid example

CH₃COOH ⇌ H⁺ + CH₃COO⁻

Ethanoic acid is only partially dissociated in water.

Embedded video tutorials

Pause after each video and complete the teacher checkpoint question.

Acids and basesCore
Indicators and pHCore
Strong vs weak acidsSupp
NeutralisationExam

Interactive practice lab

Choose a reaction type and predict the products.

Teacher checkpoint

Students should identify the reaction pattern before memorising individual examples.

  • Can name the salt formed from the acid and metal/base/carbonate.
  • Can state the correct gas test for hydrogen, carbon dioxide, or ammonia.
  • Can write a balanced symbol equation when required.

Mastery check

Auto-checks selected-response items. Written answers are teacher-marked.

1. Which gas is produced when an acid reacts with a reactive metal?
2. What is an alkali?
3. Which ionic equation represents neutralisation?

Student reflection

Use this to close the lesson and identify next steps.