What is Neutralisation?
The Question
Define neutralisation. Write its general equation. Give one example from daily life.
What Is Neutralisation?
Neutralisation is a chemical reaction in which an acid and a base react with each other to form a salt and water.
The acidic properties of the acid and the basic properties of the base are both cancelled out — the mixture becomes neutral (or closer to neutral). That’s why it’s called “neutralisation.”
Acid + Base → Salt + Water
The acid and base cancel each other out.
Why “Neutralise”?
Think of it like a tug-of-war. The acid pulls one way, the base pulls the other. If they’re equal in strength, both cancel out and the result is neutral — neither acidic nor basic.
In chemistry, when just the right amount of acid and base are mixed:
- The solution becomes neutral (pH ≈ 7)
- Neither acid nor base is left over
- Only salt and water remain
A Real Chemical Example
Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water
HCl + NaOH → NaCl + H₂O
Sodium chloride (NaCl) is common table salt — the same salt you eat! This shows that salts aren’t always harmful — they’re just the product of an acid-base reaction.
Heat Is Produced
When an acid reacts with a base, the mixture gets slightly warm. This heat produced during neutralisation is called the heat of neutralisation.
If you ever mix a strong acid with a strong base, the mixture can get quite hot. This is why we do such experiments carefully in labs.
Everyday Examples of Neutralisation
1. Antacid for Acidity
Your stomach produces hydrochloric acid (HCl) to digest food. When it produces too much, you feel acidity or heartburn — a burning sensation.
Taking an antacid (like milk of magnesia — magnesium hydroxide) helps:
Stomach acid (HCl) + Milk of magnesia (Mg(OH)₂) → Salt + Water
The antacid neutralises the excess acid. Relief follows within minutes!
This is neutralisation happening inside your own body.
2. Ant Bite Relief
An ant injects formic acid when it bites. The formic acid causes the sting.
Applying baking soda (sodium bicarbonate — a base) on the bite neutralises the formic acid:
Formic acid + Baking soda → Salt + Water + CO₂
The sting goes away as the acid is neutralised.
3. Treating Acidic Soil
Overly acidic soil reduces crop yield.
Farmers add slaked lime (calcium hydroxide) — a base — to the soil:
Soil acid + Calcium hydroxide → Salt + Water
The soil’s acidity is neutralised, making it suitable for crops.
4. Treating Factory Waste
Factories that release acidic waste must treat it before releasing into waterways.
They add a base (like lime) to neutralise the acid, preventing harm to aquatic life and the environment.
What Is a Salt?
A salt is the product formed when an acid reacts with a base. Different combinations produce different salts.
| Acid | Base | Salt formed |
|---|---|---|
| Hydrochloric acid | Sodium hydroxide | Sodium chloride (table salt) |
| Hydrochloric acid | Potassium hydroxide | Potassium chloride |
| Sulphuric acid | Sodium hydroxide | Sodium sulphate |
Salts vary widely — some are used in food, some in medicine, some in industry.
Not all salts are neutral. Some salts have slightly acidic or slightly basic properties. But in Class 7, we treat the products of neutralisation as neutral. You’ll explore salt chemistry more deeply in Class 10.
Common mistake: Writing “acid + base = no product” or “acid + base = neutral solution only.”
Neutralisation ALWAYS produces SALT + WATER. The salt and water are the products — the solution just happens to be neutral. Never leave out the products!
Try These Similar Problems
Problem 1: You mixed lemon juice and baking soda. A gas was produced and the mixture fizzed. What type of reaction is this?
Lemon juice is acidic (citric acid). Baking soda is basic (sodium bicarbonate).
When they react, it is a neutralisation reaction.
Acid + Base → Salt + Water + CO₂
The fizzing is carbon dioxide gas (CO₂) being released. This neutralisation reaction also produces CO₂ because baking soda is a carbonate.
It is a neutralisation reaction.
Problem 2: A farmer tests her soil and finds it is too basic (pH = 9). What should she add to it and why?
The soil is too basic. To neutralise it, she should add an acid.
She can add substances like gypsum (calcium sulphate) or compost (slightly acidic) to lower the pH.
The acid will neutralise the excess base, bringing the soil pH closer to neutral — suitable for most crops.
Problem 3: Write a neutralisation reaction for the antacid treatment of excess stomach acid.
Excess stomach acid is hydrochloric acid (HCl). Common antacid: Milk of magnesia — magnesium hydroxide Mg(OH)₂.
Neutralisation: HCl + Mg(OH)₂ → MgCl₂ + H₂O
Magnesium chloride (MgCl₂) is the salt formed, and water (H₂O) is also produced.
The excess acid is neutralised, providing relief from acidity.
Exam tip: “Define neutralisation with an example” is a standard 3-mark question in CBSE exams. Your answer should include: (1) definition — acid + base react to form salt + water, (2) the general equation, (3) one specific daily life example (antacid is the most commonly expected example). Write all three for full marks.