This guide covers IGCSE Chemistry topic 8 (part 1): acids, bases and salts – theory. You will revise acids (H+), bases (OH-), pH scale, indicators (litmus, phenolphthalein, methyl orange), neutralisation, and types of oxides (acidic, basic, amphoteric, neutral).

Key concepts to revise

• Acid – Contains H+; pH below 7; turns litmus red; reacts with base to form salt + water.
• Base – Contains OH- or accepts H+; pH above 7; turns litmus blue; alkali = soluble base.
• Neutralisation – Acid + base → salt + water; H+ + OH- → H2O.
• Oxides – Acidic (non-metal oxides; form acid with water); basic (metal oxides; form base with water); amphoteric (e.g. Al2O3; react with acid and base); neutral (e.g. CO, H2O).

Exam tips and command words

• State – The pH of acid, neutral, alkali; the colour of litmus in acid and alkali.
• Describe – What happens when an acid reacts with a base (salt + water); neutralisation.
• Explain – Why neutralisation is exothermic (bond making; energy released).
• Compare – Acidic oxide vs basic oxide (non-metal vs metal; acid vs base with water).

Common mistakes

• Saying bases “contain OH-” only (metal oxides are bases but insoluble; they do not contain OH- in solid form; they form OH- in reaction).
• Confusing indicator (shows pH by colour change) with universal indicator (shows full pH range).
• Not stating that neutralisation produces salt and water (and sometimes CO2 if carbonate).

Revision checklist

• State the pH range for acids, neutral and alkalis; state the colour of litmus in each.
• Write the general equation for neutralisation (acid + base → salt + water).
• Describe the reaction of an acid with a base (neutralisation); state the products.
• Classify oxides as acidic, basic, amphoteric or neutral with one example each.

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise acids and bases theory, or explore Tutopiya’s learning portal for more revision resources.