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.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial