What is a Neutralisation Reaction?- Explained - CBSE Class Notes Online

Table of Contents

What is a Neutralisation Reaction?

Have you ever mixed vinegar and baking soda and watched it fizz? This fizzing is an example of a neutralisation reaction. But what exactly is a neutralisation reaction? It’s a type of chemical reaction that happens when an acid and a base mix together. They react to form water and usually salt. This might seem like just a fun experiment, but neutralisation reactions are important in many things we do every day, from how our bodies work to how we clean our homes. In this article, we’ll explore how neutralisation reactions occur and why they’re important in our lives.

What are Chemical Reactions?

Let’s take a step back and ask, what exactly are chemical reactions? Simply put, a chemical reaction is when substances change into different substances. Everything, from rust forming on metal to digesting food in our stomachs, involves chemical reactions. In these reactions, the starting materials (called reactants) transform into new materials (called products). It’s a basic, yet crucial part of chemistry, and it’s happening all around us, every day. Now, let’s look at different types of these reactions to better understand how neutralisation fits into the picture

Types of Chemical Reactions

Chemical reactions can be categorised into several types. Understanding these helps us get a clearer view of how neutralisation, a type of acid-base reaction, works.

1. Combination Reactions

What Happens- In these reactions, two or more substances combine to form a single product.
Example- When hydrogen gas (H2) and oxygen gas (O2) combine, they form water (H2O). This reaction is expressed as 2H2 + O2 → 2H2O.

2. Decomposition Reactions

What Happens- Here, a single substance breaks down into two or more substances.
Example- When water (H2O) is broken down through electrolysis, it forms hydrogen gas (H2) and oxygen gas (O2), expressed as 2H2O → 2H2 + O2.

3. Single Replacement Reactions

What Happens- This type involves one element replacing another in a compound.
Example- If you put a strip of zinc in a copper sulphate solution (CuSO4), the zinc replaces the copper, forming zinc sulphate (ZnSO4) and copper metal (Cu). The reaction is Zn + CuSO4 → ZnSO4 + Cu.

4. Double Replacement Reactions

What Happens- In these reactions, parts of two compounds swap places to form two new compounds.
Example- Mixing silver nitrate (AgNO3) with sodium chloride (NaCl) results in the formation of silver chloride (AgCl) and sodium nitrate (NaNO3). The reaction is AgNO3 + NaCl → AgCl + NaNO3.

5. Acid-Base Reactions (Neutralisation)

What Happens- This is our main focus. In an acid-base reaction, an acid and a base react to form water and a salt.
Example- When hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), they form sodium chloride (NaCl) and water (H2O), expressed as HCl + NaOH → NaCl + H2O.

Acid-Base Reactions (Neutralisation) in Detail

Ion Exchange- In an acid-base reaction, the acid donates hydrogen ions (H+), and the base donates hydroxide ions (OH-).
Water Formation- When these ions meet, they combine to form water (H2O). This is the neutralisation process at its core.
Salt Formation- Alongside water, salt is produced. This salt is an ionic compound made from the remaining parts of the acid and base. The type of salt formed depends on the specific acid and base involved in the reaction. For instance, if sulfuric acid (H2SO4) reacts with potassium hydroxide (KOH), they produce potassium sulphate (K2SO4) and water.

Also Check – What is Neutralisation? – The Basics Explained

Components of a Neutralisation Reaction

Reactants- Acids and Bases

In a neutralisation reaction, the two key components that start the process are acids and bases.

Acids- These are substances that have a sour taste and can corrode metals. In scientific terms, acids release hydrogen ions (H+) when dissolved in water. Common examples include hydrochloric acid (HCl) in stomach acid and citric acid in fruits like lemons.
Bases- Bases are substances that can neutralise acids. They feel slippery to the touch and taste bitter. Bases release hydroxide ions (OH-) in water. Everyday examples include sodium hydroxide (NaOH), used in soaps, and baking soda (sodium bicarbonate).

Also Check – A Young Explorer’s Guide to Acids and Bases

The Reaction Process

When an acid and a base come into contact, they react chemically. The hydrogen ions (H+) from the acid meet and combine with the hydroxide ions (OH-) from the base. This union forms water (H2O).

Products- Salt and Water

Water (H2O)- This is always one of the products of a neutralisation reaction. It’s the result of hydrogen ions and hydroxide ions combining.
Salt- The other product of a neutralisation reaction is salt. But this isn’t always the salt you use in food; it can be any ionic compound that forms from the remaining parts of the acid and base. For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), they produce sodium chloride (NaCl), which is table salt.

Detailed Examples of Neutralisation Reactions

Reaction Between Hydrochloric Acid and Sodium Hydroxide

Reactants- Hydrochloric acid (HCl) and Sodium hydroxide (NaOH)
Reaction- HCl + NaOH → NaCl + H2O
Explanation- When hydrochloric acid (a common acid in stomach acid) reacts with sodium hydroxide (found in some cleaning products), they form sodium chloride (table salt) and water. The acid’s hydrogen ions (H+) combine with the base’s hydroxide ions (OH-) to form water, and the remaining sodium (Na+) and chloride (Cl-) ions form salt.

Reaction Between Acetic Acid and Calcium Hydroxide

Reactants- Acetic acid (CH3COOH) and Calcium hydroxide (Ca(OH)2)
Reaction- 2CH3COOH + Ca(OH)2 → Ca(CH3COO)2 + 2H2O
Explanation- Acetic acid, found in vinegar, reacts with calcium hydroxide, a base, to produce calcium acetate (a type of salt) and water. The acetic acid’s hydrogen ions react with the hydroxide ions from calcium hydroxide, resulting in the formation of water. The calcium ions (Ca2+) from the base combine with the acetate ions (CH3COO-) from the acid to form calcium acetate.

Reaction Between Sulfuric Acid and Potassium Hydroxide

Reactants- Sulfuric acid (H2SO4) and Potassium hydroxide (KOH)
Reaction- H2SO4 + 2KOH → K2SO4 + 2H2O
Explanation- Sulfuric acid, a strong acid, reacts with potassium hydroxide, a strong base, to form potassium sulphate (a salt) and water. The reaction involves the hydrogen ions from sulfuric acid combining with the hydroxide ions from potassium hydroxide to make water. The potassium ions (K+) and sulphate ions (SO4 2-) then form potassium sulphate.

Reaction Between Nitric Acid and Potassium Hydroxide

Reactants- Nitric Acid (HNO3) and Potassium Hydroxide (KOH)
Reaction- HNO3 + KOH → KNO3 + H2O
Explanation- When nitric acid reacts with potassium hydroxide, they form potassium nitrate (KNO3) and water. In this reaction, the hydrogen ion (H+) from the nitric acid combines with the hydroxide ion (OH-) from the potassium hydroxide to form water. The remaining nitrate ion (NO3-) and potassium ion (K+) join to create potassium nitrate, a type of salt.

Reaction Between Sulfuric Acid and Ammonium Hydroxide

Reactants- Sulfuric Acid (H2SO4) and Ammonium Hydroxide (NH4OH)
Reaction- H2SO4 + 2NH4OH → (NH4)2SO4 + 2H2O
Explanation- Sulfuric acid reacts with ammonium hydroxide to produce ammonium sulphate ((NH4)2SO4) and water. Here, two molecules of ammonium hydroxide are needed to completely neutralise one molecule of sulfuric acid. The hydrogen ions from sulfuric acid react with the hydroxide ions from ammonium hydroxide, forming water, while the sulphate ions (SO4 2-) bond with the ammonium ions (NH4+) to create ammonium sulphate.

Reaction Between Acetic Acid and Sodium Bicarbonate

Reactants- Acetic Acid (CH3COOH) and Sodium Bicarbonate (NaHCO3)
Reaction- CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
Explanation- This reaction, often observed in baking, involves acetic acid (vinegar) and sodium bicarbonate (baking soda). When they react, they form sodium acetate (CH3COONa), water, and carbon dioxide gas (CO2). The CO2 gas released is what causes the fizzing and bubbling, commonly seen when vinegar and baking soda are mixed.

Also Check – Indicators for Acid and Base- A Guide for Students

Neutralization Reaction Process

A Step-by-Step Breakdown

Let’s take a detailed look at the neutralisation process using a common example- the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH).

Reactants in Place

Hydrochloric Acid (HCl)- This is a strong acid, commonly found in stomach acid, capable of breaking down food.
Sodium Hydroxide (NaOH)- A strong base, used in various cleaning products and soaps.

Mixing Together

When HCl and NaOH are mixed, their molecules start to interact. This happens when they are dissolved in a solution like water.

Ion Exchange

Dissociation of HCl- In the solution, hydrochloric acid dissociates or splits into hydrogen ions (H+) and chloride ions (Cl-). This means HCl molecules break apart.
Dissociation of NaOH- Similarly, sodium hydroxide separates into sodium ions (Na+) and hydroxide ions (OH-). Each NaOH molecule also breaks apart.
Why Dissociation Happens- Dissociation occurs because water can break the ionic bonds holding the acid and base molecules together.

Formation of Water

Combination of Ions- The most crucial step is when the hydrogen ions (H+) from HCl meet and combine with the hydroxide ions (OH-) from NaOH.
Water Creation- This combination results in the formation of water (H2O). It’s a chemical process where two ions pair up to create a new substance – water.

Formation of Salt

Remaining Ions- After water is formed, the sodium ions (Na+) from NaOH and chloride ions (Cl-) from HCl are left.
Salt Formation- These remaining ions then come together to form sodium chloride (NaCl), which is the table salt we use in food.

Neutral Solution

Resulting pH- The solution becomes neutral, meaning it’s neither acidic nor basic. The pH level of the solution will be close to 7, which is considered neutral.

‘Why’ and ‘How’ of Neutralization

Why Acids and Bases React With Each Other

Nature of Acids- Acids are substances that have excess hydrogen ions (H+). These ions are like little packets of potential energy, looking for a way to be released or shared.
Nature of Bases- Bases, in contrast, have a surplus of hydroxide ions (OH-). These ions are like the opposite puzzle pieces to hydrogen ions, ready to combine with them.
Chemical Attraction- When acids and bases come into contact, it’s like two puzzle pieces fitting together. The hydrogen ions from the acid are attracted to the hydroxide ions from the base. This natural attraction is what drives them to react with each other.

How Neutralization Happens

Meeting of Opposites- In neutralisation, the acid and base are opposites in terms of their chemical properties. This difference is crucial because it creates a natural tendency for them to react and balance each other out.
Formation of Water- When hydrogen ions (H+) from the acid meet hydroxide ions (OH-) from the base, they bond to form water (H2O). This process reduces the number of free hydrogen and hydroxide ions in the solution.
Neutral pH- The ‘pH’ is a scale used to determine how acidic or basic a solution is. Pure water has a pH of 7, which is neutral. When an acid and base react to form water, they bring the solution towards this neutral pH.
Salt Creation- Apart from water, salt is also formed. This is the result of the remaining parts of the acid and base molecules combining. For example, if the acid was HCl and the base was NaOH, the remaining Na+ (from NaOH) and Cl- (from HCl) combine to form NaCl, which is table salt.

Why This Reaction Matters

In Our Bodies- This reaction is crucial for processes like digestion, where our stomach uses acids to break down food, and sometimes needs bases to neutralise excess acid.
In the Environment- Neutralisation helps maintain a balance in nature, such as treating acidic soil in agriculture or neutralising acidic water in rivers and lakes.

Applications of Neutralization Reaction

Health and Medicine

Antacids- Neutralise stomach acid to relieve heartburn (e.g., magnesium hydroxide or calcium carbonate).
Pharmaceutical Development- Used to create the desired pH in medications for effective absorption and metabolism.

Household and Daily Use

Cleaning Products- Neutralising acidic odours (e.g., using baking soda in refrigerators) or alkaline substances (e.g., vinegar for limescale).
Food Preparation- Baking soda neutralises acidic tastes in recipes.
Food Preservation- Using acidic substances like vinegar for pickling.
Hair and Skin Care- Shampoos and skin creams use neutralisation for pH balance.

Environmental Management

Acid Rain Neutralisation- Treatment of acidic water bodies with compounds like calcium oxide.
Soil pH Management- Adjusting soil pH for gardening and agriculture (e.g., using lime for acidic soils).

Industrial and Chemical Processes

Wastewater Treatment- Neutralising harmful acids or bases in industrial wastewater.
Chemical Manufacturing- Managing pH levels during production for safety and quality.
Environmental Protection- Mitigating acid rain effects on ecosystems.

Public Health and Safety

Hazardous Material Cleanup- Neutralization in chemical spill management.
Water Treatment- Adjusting pH of drinking water in public systems.

Agriculture and Food Industry

Agricultural Practices- Lime used to neutralise acidic soils for improved crop yield.
Cheese Making- Controlling acidity levels during cheese production.

Cosmetics and Personal Care

Soap Making- Saponification process where fats are neutralised with a base to create soap.

Scientific Research and Education

Laboratory Experiments- Demonstrating chemical principles through neutralisation reactions.

Neutralisation Reaction- Questions You Might Have

Question- Can neutralisation reactions create any gas?

Answer- Yes, some neutralisation reactions can produce gases. For example, when baking soda (a base) reacts with vinegar (an acid), carbon dioxide gas is released, causing the fizzing you see.

Question- Are there neutralisation reactions in cooking?

Answer- Definitely! For instance, when baking a cake, baking soda (a base) is used to neutralise acidic ingredients like yoghurt or lemon juice, which helps the cake rise and gives it a soft texture.

Question- Can neutralisation be used to treat pollution?

Answer- Yes, neutralisation is used to treat certain types of pollution. For example, it can neutralise acidic pollutants in water to prevent harm to aquatic life.

Question- Is it possible to neutralise every acid with any base?

Answer- In theory, yes. However, the strength and concentration of the acid and base need to be considered to achieve complete neutralisation. Also, the resulting salt must be safe and non-toxic, especially for environmental applications.

Question- Why doesn’t neutralisation happen in a battery?

Answer- Batteries are designed to use the energy from chemical reactions, not to neutralise them. In a battery, the acid and the base (or other chemicals) are kept separate to maintain a flow of electrons, which generates electricity.

Question- Can neutralisation reactions be harmful?

Answer- If strong acids or bases are involved, they need to be handled carefully. The reaction can be exothermic, releasing heat, and the products, if not handled correctly, can be hazardous.

Question- Do all neutralisation reactions happen quickly?

Answer- The speed of neutralisation reactions can vary. While many happen almost instantly, some reactions, especially those involving weaker acids or bases, can take longer.

Question- Are neutralisation reactions reversible?

Answer- Most neutralisation reactions are considered irreversible. Once the acid and base react to form water and a salt, they usually can’t be turned back into their original forms.