This reference lists common acids, bases and salts with their formulae and whether each is strong or weak. An acid gives hydrogen ions in water, a base neutralises acid, and an alkali is a soluble base that gives hydroxide ions.
The Acids, Bases and Salts chapter turns on knowing a small set of common substances: which acids and alkalis are strong or weak, and the formulae of the salts you prepare from them. An acid produces hydrogen ions in water, a base is a metal oxide or hydroxide that neutralises an acid, and an alkali is a base that dissolves to give hydroxide ions. This reference lists the common examples you meet in SPM Chemistry, arranged the way the DSKP presents them, so you can name, write formulae and predict reactions.
Scope note
The tables below hold the standard KSSM examples for Form 4. Learn each formula together with whether the acid or alkali is strong or weak, because that difference decides the pH, the rate of reaction and the outcome of many questions. Use the tables beside the salt-preparation and neutralisation topics.
Common acids
| Acid | Formula | Strength | Note |
|---|---|---|---|
| Hydrochloric acid | HCl | Strong | Monoprotic; one replaceable hydrogen |
| Sulfuric acid | H2SO4 | Strong | Diprotic; two replaceable hydrogens |
| Nitric acid | HNO3 | Strong | Monoprotic |
| Ethanoic acid | CH3COOH | Weak | Partially ionised; found in vinegar |
| Carbonic acid | H2CO3 | Weak | Formed when carbon dioxide dissolves in water |
Common bases and alkalis
| Base / alkali | Formula | Strength / solubility |
|---|---|---|
| Sodium hydroxide | NaOH | Strong alkali (soluble) |
| Potassium hydroxide | KOH | Strong alkali (soluble) |
| Calcium hydroxide | Ca(OH)2 | Alkali (slightly soluble) |
| Ammonia solution | NH3 (aq) | Weak alkali |
| Copper(II) oxide | CuO | Base (insoluble) |
| Magnesium oxide | MgO | Base (insoluble) |
Common salts
| Salt | Formula | Use or note |
|---|---|---|
| Sodium chloride | NaCl | Table salt; food seasoning |
| Potassium nitrate | KNO3 | Fertiliser |
| Copper(II) sulfate | CuSO4 | Blue crystals; used in experiments |
| Calcium carbonate | CaCO3 | Marble and limestone |
| Ammonium sulfate | (NH4)2SO4 | Nitrogen fertiliser |
How to use the tables
Combine an acid with a base or alkali and the products are a salt and water. For example, hydrochloric acid and sodium hydroxide give sodium chloride and water: HCl(aq) + NaOH(aq) gives NaCl(aq) + H2O(l). The acid used decides the salt type: hydrochloric acid gives a chloride, sulfuric acid a sulfate, and nitric acid a nitrate. Whether an acid is strong or weak decides its pH and how fast it reacts, while whether a base is soluble decides whether you call it an alkali and how you use it to prepare a salt.
pH and indicators
These acids and alkalis also anchor the pH scale, which the chapter tests closely. A strong acid has a low pH, close to 1, because it ionises fully to give a high concentration of hydrogen ions; a weak acid such as ethanoic acid has a higher pH at the same concentration because it ionises only partially. Pure water is neutral at pH 7, a weak alkali such as ammonia solution sits a little above 7, and a strong alkali such as sodium hydroxide is close to pH 14. You can identify these with indicators: litmus turns red in acid and blue in alkali, while phenolphthalein is colourless in acid and pink in alkali. Being able to link a substance from the tables to its pH and its indicator colour is exactly what many structured questions ask.
Common mistakes to avoid
- Treating strong and weak acids as the same; a strong acid ionises fully and has a lower pH at the same concentration.
- Confusing base and alkali; an alkali is a soluble base.
- Forgetting that sulfuric acid is diprotic, so it can react with twice as much alkali.
- Writing the wrong salt for the acid used, such as a sulfate from hydrochloric acid.
How we help
Our online one-to-one teachers connect these substances to neutralisation, salt preparation and the pH scale, so you can predict the products of any acid-base reaction. Lessons are in English, one to one, from RM50 per hour, with a paid one-hour trial. Because the Acids, Bases and Salts chapter runs through both papers, knowing these common examples well gives you a reliable base for its calculations and its practical work.
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