Acids, Bases and Salts: Class 10 Chemistry Guide
Acids, bases and salts are everywhere — in the lemon you squeeze, the soap you wash with, and the common salt on your plate. This chapter is a scoring favourite in Class 10 chemistry because the ideas are clear once you learn the basics. This guide explains what acids and bases are, how the pH scale works, how indicators detect them, what happens during neutralisation, and the common examples you must know.
What are acids and bases?
An acid is a substance that tastes sour and produces hydrogen ions (H⁺) when dissolved in water. Examples include the citric acid in lemons and the hydrochloric acid in your stomach.
A base is a substance that tastes bitter, feels soapy, and produces hydroxide ions (OH⁻) when dissolved in water. A base that dissolves in water is called an alkali, such as sodium hydroxide. Never taste chemicals in the lab — these descriptions are for understanding only.
Indicators: how to tell them apart
An indicator is a substance that changes colour to show whether something is an acid or a base. The most common ones in school labs are:
- Litmus: turns red in acid and blue in base. Blue litmus turns red in acid; red litmus turns blue in base.
- Methyl orange: red in acid, yellow in base.
- Phenolphthalein: colourless in acid, pink in base.
- Natural indicators: such as turmeric (yellow, turns red in base) and red cabbage juice.
The pH scale
The pH scale measures how acidic or basic a solution is, on a range from 0 to 14. It is based on the concentration of hydrogen ions in the solution.
| pH value | Nature | Example |
|---|---|---|
| 0 to 6 | Acidic | Lemon juice, vinegar |
| 7 | Neutral | Pure water |
| 8 to 14 | Basic (alkaline) | Soap, baking soda solution |
A lower pH means a stronger acid, and a higher pH means a stronger base. A change of one pH unit means a tenfold change in acidity. The pH of our blood, soil, and even toothpaste all matter in daily life.
Neutralisation reaction
When an acid reacts with a base, they cancel out each other's properties to form a salt and water. This is called a neutralisation reaction.
Acid + Base → Salt + Water
For example, hydrochloric acid reacts with sodium hydroxide to give common salt and water (HCl + NaOH → NaCl + H₂O). Neutralisation explains why antacids relieve acidity in the stomach and why lime is added to acidic soil.
What are salts?
A salt is the compound formed when the hydrogen ion of an acid is replaced by a metal ion from a base. Salts can be neutral, acidic, or basic depending on the acid and base that made them. Some important salts you should know:
- Sodium chloride (NaCl): common table salt, used in cooking and to make other chemicals.
- Sodium hydrogen carbonate (baking soda): used in baking and in fire extinguishers.
- Sodium carbonate (washing soda): used for cleaning and softening hard water.
- Calcium sulphate (plaster of Paris): used to set fractured bones and to make decorative items.
Everyday examples
- Acids: vinegar (acetic acid), curd (lactic acid), and the acid in soft drinks (carbonic acid).
- Bases: soap, toothpaste, and milk of magnesia used to treat acidity.
- Salts: table salt, baking soda, and the gypsum used in building materials.
Common mistakes to avoid
- Thinking all bases are alkalis — only bases that dissolve in water are alkalis.
- Assuming a lower pH means more basic — a lower pH means more acidic.
- Forgetting that neutralisation always produces both a salt and water.
Want to test yourself? Try the LearnIQ practice quiz for more chemistry questions, or browse all study guides.