Multiple choiceQuestion 1 · Recall
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By the end you can name and write the formulas of the four common acids (HCl, H₂SO₄, HNO₃, CH₃COOH) and the three common alkalis (NaOH, KOH, NH₃), and you know when to add state symbols.
Cambridge picked the acids and bases that show up constantly in exam questions, practicals, and real chemistry. Memorise them now and you save brain-space later.
Acid (for this topic)
A substance that donates protons (H⁺ ions) in aqueous solution. The four you must know: hydrochloric, sulfuric, nitric, and ethanoic acid.
Alkali (for this topic)
A soluble base that releases hydroxide ions (OH⁻) in water. The three you must know: sodium hydroxide, potassium hydroxide, and ammonia.
| name | formula | everyday context |
|---|---|---|
| Hydrochloric acid | Stomach acid, pickling steel | |
| Sulfuric acid | Car batteries, fertiliser production | |
| Nitric acid | Explosives, fertilisers, etching | |
| Ethanoic acid | Vinegar (≈5 %), food preservation |
Key detail: is diprotic — it can donate two protons, one after the other. The other three are monoprotic (one proton each).
| name | formula | everyday context |
|---|---|---|
| Sodium hydroxide | Drain cleaner, soap making | |
| Potassium hydroxide | Biodegradable soaps, batteries | |
| Ammonia | Cleaning products, fertiliser precursor |
Watch out: ammonia isn't a hydroxide — it accepts a proton from water to make and . That's why it fits the Brønsted–Lowry definition perfectly (coming up next).