Class 10 Science Notes Chapter 2 'Acids, Bases and Salts': Complete Notes and Examples

Acids, bases and salts are an important part of everyday life, from the food we eat and medicines we take to the cleaning products and chemicals used in industries. In Class 10 Science Chapter 2, students learn about the properties of acids and bases, indicators, chemical reactions, pH scale, salts and their practical applications.

These notes are designed to simplify the Class 10 Science Notes Chapter 2 Acids, Bases and Salts with easy explanations, important reactions and key concepts for quick revision before exams. 

Topics Covered in Class 10 Science NOTES Chapter 2 Acids, Bases and Salts 

What are Acids, Bases and Salts	Strength of Acids and Bases
Properties of Acids	Neutralisation Reaction
Properties of Bases	Salts
Chemical Reactions of Acids and Bases	Common Salts and Their Uses
Indicators	Water of Crystallisation
The pH Scale	Important Chemical Equations
Importance of pH in Everyday Life	—

Class 10 Science Chapter 2: Acids, Bases and Salts 

What are Acids, Bases and Salts

Acids, bases and salts are three important classes of chemical substances with different properties and uses. They are commonly found in our daily lives, from lemon juice and vinegar to soap, toothpaste, baking soda and common salt.

• Acids release hydrogen ions (H⁺) in aqueous solutions.
• Bases release hydroxide ions (OH⁻) in aqueous solutions.
• Salts are formed when an acid reacts with a base in a neutralisation reaction.

Examples 

Acids	Bases	Salts
Hydrochloric acid (HCl)	Sodium hydroxide (NaOH)	Sodium chloride (NaCl)
Sulphuric acid (H₂SO₄)	Calcium hydroxide [Ca(OH)₂]	Baking soda (NaHCO₃)
Nitric acid (HNO₃)	Potassium hydroxide (KOH)	Washing soda (Na₂CO₃·10H₂O)

Properties of Acids

Acids have characteristic physical and chemical properties that help identify them.

Property	Description
Taste	Sour in taste (Never taste chemicals in the laboratory.)
Effect on Litmus Paper	Turn blue litmus paper red.
Electrical Conductivity	Conduct electricity in aqueous solutions due to the presence of ions.
Reaction with Metals	React with metals to produce hydrogen gas.
Reaction with Bases	React with bases to form salt and water (neutralisation reaction).
pH Value	Have a pH value less than 7.

Properties of Bases

Bases are substances that neutralise acids and have their own characteristic properties.

Properties of Bases

Property	Description
Taste	Bitter in taste. (Do not taste chemicals in the laboratory.)
Texture	Feel soapy or slippery to touch. (Avoid touching chemicals directly.)
Effect on Litmus Paper	Turn red litmus paper blue.
Electrical Conductivity	Conduct electricity in aqueous solutions due to the presence of ions.
pH Value	Have a pH value greater than 7.

Common Examples of Bases

Base	Chemical Formula
Sodium Hydroxide	NaOH
Potassium Hydroxide	KOH
Calcium Hydroxide	Ca(OH)₂
Ammonium Hydroxide	NH₄OH

Chemical Reactions of Acids and Bases

1. Acid + Metal → Salt + Hydrogen Gas

When an acid reacts with a metal, hydrogen gas is evolved.

Example

Zn + 2HCl → ZnCl₂ + H₂↑

2. Acid + Metal Carbonate → Salt + Water + Carbon Dioxide

Acids react with metal carbonates to produce carbon dioxide gas.

Example

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑

3. Acid + Metal Hydrogen Carbonate → Salt + Water + Carbon Dioxide

Example

NaHCO₃ + HCl → NaCl + H₂O + CO₂↑

4. Acid + Base → Salt + Water

This reaction is called a neutralisation reaction.

Example

HCl + NaOH → NaCl + H₂O

Indicators

Indicators are substances that change colour in acidic or basic solutions.

Types of Indicators

Indicator	Acid	Base
Blue Litmus	Turns Red	No Change
Red Litmus	No Change	Turns Blue
Phenolphthalein	Colourless	Pink
Methyl Orange	Red	Yellow
Universal Indicator	Different colours depending on pH	Different colours depending on pH

Indicators help determine whether a solution is acidic, basic, or neutral.

The pH Scale

The pH scale measures how acidic or basic a solution is. Its values range from 0 to 14.

pH Value	Nature
0–6	Acidic
7	Neutral
8–14	Basic

Importance of pH in Everyday Life

• Our stomach contains hydrochloric acid for digestion.
• Tooth decay begins when the mouth's pH falls below 5.5.
• Farmers test soil pH before growing crops.
• The human body functions best at a specific pH range.

Strength of Acids and Bases

The strength of an acid or base depends on the number of ions it produces in water. Strong acids and bases ionise completely, whereas weak acids and bases ionise only partially. 

Type	Characteristics	Examples
Strong Acids	Ionise completely in water and produce a large number of H⁺ ions.	Hydrochloric Acid (HCl), Nitric Acid (HNO₃), Sulphuric Acid (H₂SO₄)
Weak Acids	Ionise partially in water and produce fewer H⁺ ions.	Acetic Acid (CH₃COOH), Citric Acid, Carbonic Acid (H₂CO₃)
Strong Bases	Ionise completely in water and produce a large number of OH⁻ ions.	Sodium Hydroxide (NaOH), Potassium Hydroxide (KOH)
Weak Bases	Ionise partially in water and produce fewer OH⁻ ions.	Ammonium Hydroxide (NH₄OH)

Neutralisation Reaction

A neutralisation reaction occurs when an acid reacts with a base to form salt and water.

General Equation

Acid + Base → Salt + Water

Example

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

Neutralisation reactions are widely used in:

• Treating acidic soil
• Manufacturing medicines
• Treating insect stings
• Wastewater treatment

Salts

Salts are ionic compounds formed during neutralisation reactions.They are composed of positive and negative ions and have a wide range of industrial and household applications.

Common Salts and Their Uses

1. Common Salt (Sodium Chloride)

Formula: NaCl

Uses:Food seasoning,Food preservation,Manufacture of chemicals

2. Baking Soda

Formula: NaHCO₃

Uses:Baking powder,Antacid and Fire extinguishers

3. Washing Soda

Formula: Na₂CO₃·10H₂O

Uses:Cleaning agent,Softening hard water and Glass and soap industries

4. Bleaching Powder

Formula: CaOCl₂

Uses:Disinfecting drinking water,Bleaching cotton and paper and Sanitising swimming pools

5. Plaster of Paris (POP)

Formula: CaSO₄·½H₂O

Uses:Making statues,Surgical casts,Decorative designs and False ceilings

Water of Crystallisation

Water of crystallisation is the fixed number of water molecules chemically attached to a salt crystal.

Examples

• Washing soda – Na₂CO₃·10H₂O
• Gypsum – CaSO₄·2H₂O

These water molecules help maintain the crystal structure of salts.

Important Chemical Equations

Reaction	Chemical Equation
Acid + Metal	Zn + 2HCl → ZnCl₂ + H₂↑
Acid + Carbonate	CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑
Neutralisation	HCl + NaOH → NaCl + H₂O
Baking Soda	NaHCO₃ + HCl → NaCl + H₂O + CO₂↑
Formation of POP	CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O