Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want the characteristic properties of acids and bases — pH, indicators and typical reactions — to become a reliable source of marks instead of a colour-memorising exercise.
What query it owns: how to understand and revise the characteristic properties of acids and bases in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the acids-and-bases-properties revision-guide angle, while Tutopiya’s The Characteristic Properties Of Acids And Bases subtopic page owns the learning resource and the free Acids And Bases quiz owns the practice.

Acids and bases have distinctive chemical properties that Cambridge IGCSE Coordinated Science (0654) tests every year. You need to know the pH scale, indicator colour changes, and how acids react with metals, metal oxides, hydroxides and carbonates. This guide links each property to the equations and observations examiners expect.

Key takeaways

• Acids have pH < 7; bases/alkalis have pH > 7; neutral = pH 7.
• Acids release H⁺ ions in aqueous solution; alkalis release OH⁻ ions.
• Acids react with metals (above hydrogen in reactivity) → salt + hydrogen gas.
• Acids react with metal oxides/hydroxides → salt + water (neutralisation).
• Acids react with carbonates → salt + water + carbon dioxide.

What are the characteristic properties of acids and bases in Cambridge IGCSE Coordinated Science?

Acids are proton (H⁺) donors in solution; bases accept protons or produce OH⁻ ions. Alkalis are soluble bases. The pH scale measures acidity from 0 (strong acid) to 14 (strong alkali). Indicators change colour depending on pH, and characteristic reactions produce salts plus identifiable products like H₂ or CO₂.

You can read the full explanation, equations and notes on Tutopiya’s The Characteristic Properties Of Acids And Bases subtopic page before you attempt questions.

pH scale and indicators

pH range	Description	Universal indicator colour
0–3	Strong acid	Red
4–6	Weak acid	Orange / yellow
7	Neutral	Green
8–11	Weak alkali	Blue
12–14	Strong alkali	Purple

Indicator	In acid	In alkali
Litmus	Red	Blue
Methyl orange	Red	Yellow
Phenolphthalein	Colourless	Pink

Typical acid reactions

Reactant	Products	Observation
Metal (e.g. Mg, Zn)	Salt + H₂	Effervescence
Metal oxide / hydroxide	Salt + H₂O	Solid dissolves; neutralisation
Metal carbonate	Salt + H₂O + CO₂	Effervescence; limewater turns milky
Ammonia solution	Ammonium salt	No gas; neutralisation

Acids and bases in past-paper wording

Command word	What the question wants	Typical stem
State	pH, product or observation	”State the products when HCl reacts with CaCO₃.”
Write equation	Balanced symbol equation	”Write an equation for zinc and sulfuric acid.”
Describe	Test or colour change	”Describe the colour of litmus in an alkali.”
Explain	Why reaction occurs / does not	”Explain why copper does not react with dilute acid.”

Worked exam-style stems

1. “Write a word equation for the reaction of hydrochloric acid with calcium carbonate.” Calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide. Reward: correct reactants and all three products.
2. “State the pH of a neutral solution.” pH 7. Reward: value 7.
3. “Explain why effervescence is seen when an acid reacts with a metal carbonate.” Carbon dioxide gas is produced and escapes from the solution. Reward: CO₂ + gas evolved.

Test yourself with the Acids And Bases quiz once you can write acid reaction equations from memory.

How acids and bases connect to the syllabus

Acid-base chemistry leads to salt preparation, oxide classification and ion tests. Neutralisation links to energy changes (exothermic). The Cambridge IGCSE Coordinated Science resource hub links every Acids, Bases And Salts subtopic.

Common mistakes students make

• Confusing bases (insoluble) with alkalis (soluble bases).
• Writing H₂ as a product when acid reacts with a metal oxide (product is water only).
• Forgetting copper, silver and gold do not react with dilute acids.
• Stating all acids have pH 0 (strong acids are low pH; weak acids are higher).
• Mixing up litmus colours in acid vs alkali.

When you need more support

If acid reaction equations keep costing marks, work through the Acids And Bases quiz, then get focused help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

Is acids and bases hard in Coordinated Science? The reaction patterns repeat — learn the four acid reactions and indicator colours.

What is the difference between a base and an alkali? A base neutralises acids; an alkali is a soluble base that releases OH⁻ ions in water.

What gas is produced when an acid reacts with a carbonate? Carbon dioxide (CO₂).

How do I revise acids and bases effectively? Memorise pH, indicators and the four reaction types with equations, then take the quiz.

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