Introduction

Acids, bases, and salts are among the most important substances we encounter in our daily lives. From the lemon juice we drink and the vinegar used in cooking to the soap we use for cleaning and the medicines that relieve acidity, these substances play a vital role in our everyday activities.

In this chapter, you will learn how to identify acids and bases using different indicators, understand their physical and chemical properties, explore the concept of the pH scale, and discover how neutralisation reactions occur. You will also study the preparation and uses of important salts such as baking soda, washing soda, bleaching powder, and plaster of Paris, along with their applications in homes, industries, and healthcare.

These Class 10 Science notes are designed according to the latest CBSE syllabus and explain every concept in simple, student-friendly language. With easy explanations, balanced chemical equations, real-life examples, exam tips, and quick revision points, these notes will help you build a strong conceptual foundation and prepare effectively for school and board examinations.

Learning Objectives

After studying this chapter, you will be able to:

• Understand the meaning of acids, bases, and salts.
• Identify the physical and chemical properties of acids and bases.
• Differentiate between strong and weak acids as well as strong and weak bases.
• Explain how natural, synthetic, and olfactory indicators help identify acidic and basic substances.
• Write and understand the chemical reactions of acids and bases with metals, metal carbonates, metal bicarbonates, and metal oxides.
• Understand the concept of neutralisation and its practical applications.
• Explain the pH scale and its importance in everyday life.
• Describe the role of pH in digestion, tooth decay, soil health, and self-defence mechanisms of plants and animals.
• Learn about the preparation, properties, and uses of important salts such as baking soda, washing soda, bleaching powder, and plaster of Paris.
• Solve board exam questions confidently using important definitions, reactions, and revision tips.

What Are Acids?

Acids are substances that produce hydrogen ions (H⁺) when dissolved in water. They usually have a sour taste and can react with metals to produce hydrogen gas. Many naturally occurring substances, such as lemon juice and vinegar, are acidic.

Definition

An acid is a substance that releases hydrogen ions (H⁺) in an aqueous solution.

Common Examples of Acids

Physical Properties of Acids

Acids possess several characteristic physical properties that help in their identification.

1. Sour Taste

Most acids have a sour taste.

Examples:

• Lemon
• Orange
• Tamarind
• Vinegar

Note: Never taste chemicals in a laboratory to identify them.

2. Conduct Electricity

Acidic solutions conduct electricity because they contain free hydrogen ions (H⁺).

This property makes them electrolytes.

3. Corrosive Nature

Strong acids can corrode metals and damage skin, clothing, and laboratory equipment if handled carelessly.

Examples include:

• Sulphuric acid
• Nitric acid

Always handle acids with proper safety precautions.

4. Turn Blue Litmus Red

Blue litmus paper changes to red when dipped in an acidic solution.

This is one of the simplest tests to identify an acid.

5. pH Less Than 7

Acidic solutions have a pH value below 7.

The lower the pH value, the stronger the acid.

Strong and Weak Acids

Acids are classified based on the extent to which they ionise in water.

Did You Know?

The human stomach secretes hydrochloric acid (HCl), which helps digest food and destroys harmful microorganisms. To prevent damage to the stomach lining, the stomach produces a protective layer of mucus.

Exam Tip

Remember: All acids contain hydrogen, but not all hydrogen-containing compounds behave as acids. For example, glucose (C₆H₁₂O₆) and alcohol (C₂H₅OH) contain hydrogen but do not release H⁺ ions in water, so they are not acids.

What Are Bases?

Bases are substances that produce hydroxide ions (OH⁻) when dissolved in water. They are generally bitter in taste and have a slippery or soapy feel. Bases are commonly found in soaps, detergents, toothpaste, and many household cleaning products.

Bases play an important role in neutralising acids and are widely used in industries, agriculture, medicine, and everyday life.

Definition

A base is a substance that releases hydroxide ions (OH⁻) in an aqueous solution.

Common Examples of Bases

Physical Properties of Bases

Bases have several characteristic properties that help distinguish them from acids.

1. Bitter Taste

Most bases have a bitter taste.

Examples:

• Baking soda solution
• Soap solution

Safety Note: Never taste chemicals in a laboratory.

2. Slippery or Soapy Feel

Bases feel slippery when touched because they react with the natural oils present on the skin.

Examples:

• Soap solution
• Detergent solution

3. Turn Red Litmus Blue

A base changes red litmus paper to blue.

This is one of the simplest tests used to identify a basic solution.

4. Conduct Electricity

Aqueous solutions of bases conduct electricity because they contain free hydroxide ions (OH⁻).

Therefore, bases are also electrolytes.

5. pH Greater Than 7

Basic solutions have a pH value greater than 7.

The higher the pH value, the stronger the base.

Strong and Weak Bases

Bases are classified according to the extent to which they produce hydroxide ions in water.

Difference Between Strong and Weak Bases

What Are Indicators?

Indicators are substances that help determine whether a solution is acidic, basic, or neutral by changing colour or producing a characteristic smell.

They are commonly used in laboratories, industries, and educational experiments.

Definition

An indicator is a substance that changes colour or smell in acidic and basic solutions.

Types of Indicators

Indicators are classified into three main categories:

1. Natural Indicators
2. Synthetic Indicators
3. Olfactory Indicators

1. Natural Indicators

Natural indicators are obtained from plants and other natural sources.

(a) Litmus

Litmus is extracted from lichens and is the most commonly used natural indicator.

Colour Change

(b) Turmeric

Turmeric acts as a natural indicator.

(c) China Rose (Hibiscus)

Extract from China rose flowers acts as a natural indicator.

2. Synthetic Indicators

Synthetic indicators are man-made chemicals used in laboratories for accurate testing.

(a) Phenolphthalein

(b) Methyl Orange

Difference Between Phenolphthalein and Methyl Orange

3. Olfactory Indicators

Olfactory indicators are substances whose smell changes in acidic and basic solutions.

Common Olfactory Indicators

• Onion
• Vanilla essence
• Clove oil

Observation

Summary of Indicators

Everyday Uses of Indicators

• Testing soil pH in agriculture
• Water quality testing
• Laboratory experiments
• Medical diagnosis
• Food industry
• Chemical manufacturing

Did You Know?

The pH paper used in science laboratories is made by combining several indicators. This allows it to display different colours over a wide range of pH values, making it more accurate than using a single indicator.

Exam Tip

Remember these colour changes:

• Blue Litmus → Red in Acid
• Red Litmus → Blue in Base
• Phenolphthalein → Pink in Base
• Methyl Orange → Red in Acid
• Turmeric → Reddish-Brown in Base

These are among the most frequently tested concepts in CBSE Class 10 Science examinations.

Quick Revision

• Bases release OH⁻ ions in water.
• Bases are bitter, slippery, and have a pH greater than 7.
• Strong bases ionise completely, while weak bases ionise only partially.
• Indicators help identify acidic and basic solutions.
• Natural indicators include litmus, turmeric, and China rose.
• Synthetic indicators include phenolphthalein and methyl orange.
• Olfactory indicators such as onion, vanilla, and clove oil change their smell in basic solutions.

What Are Bases?

Bases are substances that produce hydroxide ions (OH⁻) when dissolved in water. They are generally bitter in taste and have a slippery or soapy feel. Bases are commonly found in soaps, detergents, toothpaste, and many household cleaning products.

Bases play an important role in neutralising acids and are widely used in industries, agriculture, medicine, and everyday life.

Definition

A base is a substance that releases hydroxide ions (OH⁻) in an aqueous solution.

Common Examples of Bases

Physical Properties of Bases

Bases have several characteristic properties that help distinguish them from acids.

1. Bitter Taste

Most bases have a bitter taste.

Examples:

• Baking soda solution
• Soap solution

Safety Note: Never taste chemicals in a laboratory.

2. Slippery or Soapy Feel

Bases feel slippery when touched because they react with the natural oils present on the skin.

Examples:

• Soap solution
• Detergent solution

3. Turn Red Litmus Blue

A base changes red litmus paper to blue.

This is one of the simplest tests used to identify a basic solution.

4. Conduct Electricity

Aqueous solutions of bases conduct electricity because they contain free hydroxide ions (OH⁻).

Therefore, bases are also electrolytes.

5. pH Greater Than 7

Basic solutions have a pH value greater than 7.

The higher the pH value, the stronger the base.

Strong and Weak Bases

Bases are classified according to the extent to which they produce hydroxide ions in water.

Difference Between Strong and Weak Bases

What Are Indicators?

Indicators are substances that help determine whether a solution is acidic, basic, or neutral by changing colour or producing a characteristic smell.

They are commonly used in laboratories, industries, and educational experiments.

Definition

An indicator is a substance that changes colour or smell in acidic and basic solutions.

Types of Indicators

Indicators are classified into three main categories:

1. Natural Indicators
2. Synthetic Indicators
3. Olfactory Indicators

1. Natural Indicators

Natural indicators are obtained from plants and other natural sources.

(a) Litmus

Litmus is extracted from lichens and is the most commonly used natural indicator.

Colour Change

(b) Turmeric

Turmeric acts as a natural indicator.

(c) China Rose (Hibiscus)

Extract from China rose flowers acts as a natural indicator.

2. Synthetic Indicators

Synthetic indicators are man-made chemicals used in laboratories for accurate testing.

(a) Phenolphthalein

(b) Methyl Orange

Difference Between Phenolphthalein and Methyl Orange

3. Olfactory Indicators

Olfactory indicators are substances whose smell changes in acidic and basic solutions.

Common Olfactory Indicators

• Onion
• Vanilla essence
• Clove oil

Observation

Summary of Indicators

Everyday Uses of Indicators

• Testing soil pH in agriculture
• Water quality testing
• Laboratory experiments
• Medical diagnosis
• Food industry
• Chemical manufacturing

Did You Know?

The pH paper used in science laboratories is made by combining several indicators. This allows it to display different colours over a wide range of pH values, making it more accurate than using a single indicator.

Exam Tip

Remember these colour changes:

• Blue Litmus → Red in Acid
• Red Litmus → Blue in Base
• Phenolphthalein → Pink in Base
• Methyl Orange → Red in Acid
• Turmeric → Reddish-Brown in Base

These are among the most frequently tested concepts in CBSE Class 10 Science examinations.

Quick Revision

• Bases release OH⁻ ions in water.
• Bases are bitter, slippery, and have a pH greater than 7.
• Strong bases ionise completely, while weak bases ionise only partially.
• Indicators help identify acidic and basic solutions.
• Natural indicators include litmus, turmeric, and China rose.
• Synthetic indicators include phenolphthalein and methyl orange.
• Olfactory indicators such as onion, vanilla, and clove oil change their smell in basic solutions.

Chemical Properties of Acids and Bases

Chemical properties describe how acids and bases react with other substances. These reactions are among the most important topics in the CBSE Class 10 Science syllabus and are frequently tested in board examinations.

In this section, you will learn how acids and bases react with metals, metal carbonates, metal bicarbonates, metal oxides, and non-metal oxides. You will also study the neutralisation reaction, which is widely used in everyday life and various industries.

1. Reaction of Acids with Metals

When acids react with metals, they produce salt and hydrogen gas.

General Equation

Acid + Metal → Salt + Hydrogen Gas (H₂)

Example 1

Zn + 2HCl → ZnCl₂ + H₂↑

Observation:

• Bubbles of hydrogen gas are produced.
• Zinc gradually dissolves in hydrochloric acid.
• The reaction is exothermic (heat is released).

Example 2

Mg + 2HCl → MgCl₂ + H₂↑

Magnesium reacts vigorously with hydrochloric acid to produce hydrogen gas.

Test for Hydrogen Gas

Hydrogen gas burns with a ‘pop’ sound when a burning splint is brought near it.

This is the standard laboratory test for identifying hydrogen gas.

Important Note

Not all metals react with dilute acids.

For example:

• Copper (Cu)
• Silver (Ag)
• Gold (Au)

These metals are less reactive and do not react with dilute hydrochloric acid.

2. Reaction of Acids with Metal Carbonates

Acids react with metal carbonates to produce:

• Salt
• Water
• Carbon dioxide gas

General Equation

Acid + Metal Carbonate → Salt + Water + Carbon Dioxide

Example

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑

Observation

• Brisk effervescence is observed.
• Carbon dioxide gas is evolved.

Test for Carbon Dioxide

Pass the gas through lime water.

CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

Observation:

Lime water turns milky due to the formation of calcium carbonate.

3. Reaction of Acids with Metal Bicarbonates

Metal bicarbonates also react with acids to produce:

• Salt
• Water
• Carbon dioxide gas

General Equation

Acid + Metal Bicarbonate → Salt + Water + Carbon Dioxide

Example

NaHCO₃ + HCl → NaCl + H₂O + CO₂↑

Everyday Example

Baking soda reacts with lemon juice or vinegar, releasing carbon dioxide gas. This reaction makes cakes and bread soft and fluffy.

Difference Between Carbonates and Bicarbonates

4. Reaction of Acids with Metal Oxides

Metal oxides are generally basic in nature.

They react with acids to produce:

• Salt
• Water

General Equation

Acid + Metal Oxide → Salt + Water

Example

CuO + 2HCl → CuCl₂ + H₂O

Observation

• Black copper oxide dissolves.
• Blue-green copper chloride solution is formed.

Another Example

MgO + 2HCl → MgCl₂ + H₂O

Why Are Metal Oxides Called Basic Oxides?

Metal oxides neutralise acids to produce salt and water.

Therefore, they behave like bases.

5. Reaction of Bases with Non-Metal Oxides

Non-metal oxides are generally acidic in nature.

They react with bases to form:

• Salt
• Water

General Equation

Base + Non-Metal Oxide → Salt + Water

Example

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Observation

• White precipitate of calcium carbonate is formed.
• Lime water turns milky.

Why Are Non-Metal Oxides Called Acidic Oxides?

They react with bases just as acids do.

Hence, they are known as acidic oxides.

6. Neutralisation Reaction

One of the most important chemical reactions involving acids and bases is the neutralisation reaction.

Definition

A neutralisation reaction is a chemical reaction in which an acid reacts with a base to produce salt and water.

General Equation

Acid + Base → Salt + Water

Example

HCl + NaOH → NaCl + H₂O

Hydrochloric acid reacts with sodium hydroxide to form sodium chloride (common salt) and water.

Another Example

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

Characteristics of Neutralisation

• Heat is released (exothermic reaction).
• Salt and water are formed.
• The acidic and basic properties are neutralised.

Everyday Applications of Neutralisation

1. Indigestion

Excess hydrochloric acid in the stomach causes acidity.

Antacids such as Milk of Magnesia (Mg(OH)₂) neutralise the excess acid and provide relief.

2. Ant Bite

An ant bite injects formic acid into the skin.

Applying baking soda paste or calamine lotion helps neutralise the acid and reduces irritation.

3. Soil Treatment

• Acidic soil is treated with quick lime (CaO) or slaked lime [Ca(OH)₂].
• Basic soil is treated with organic compost to reduce alkalinity.

4. Factory Waste

Industrial waste often contains acids.

These acidic wastes are neutralised before being released into rivers to reduce environmental pollution.

Summary of Important Reactions

Important Chemical Equations

Zinc with Hydrochloric Acid

Zn + 2HCl → ZnCl₂ + H₂↑

Calcium Carbonate with Hydrochloric Acid

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑

Sodium Bicarbonate with Hydrochloric Acid

NaHCO₃ + HCl → NaCl + H₂O + CO₂↑

Copper Oxide with Hydrochloric Acid

CuO + 2HCl → CuCl₂ + H₂O

Carbon Dioxide with Lime Water

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Neutralisation Reaction

HCl + NaOH → NaCl + H₂O

Did You Know?

Fire extinguishers used for electrical and oil fires often contain sodium hydrogen carbonate (baking soda). When heated, it releases carbon dioxide gas, which helps smother the fire by cutting off the oxygen supply.

Exam Tip

Memorise the products formed in each type of reaction. In board exams, questions often ask you to identify the products or complete a chemical equation. Understanding the reaction pattern is more effective than rote memorisation.

Quick Revision

• Acids react with metals to produce salt and hydrogen gas.
• Acids react with metal carbonates and bicarbonates to produce salt, water, and carbon dioxide.
• Acids react with metal oxides to form salt and water.
• Bases react with non-metal oxides to produce salt and water.
• Neutralisation is the reaction between an acid and a base, producing salt and water.
• Carbon dioxide turns lime water milky.
• Hydrogen gas burns with a characteristic ‘pop’ sound.

The pH Scale and Its Importance in Everyday Life

The strength of acids and bases can be measured using the pH scale. The term pH stands for “potential of Hydrogen”, which indicates the concentration of hydrogen ions (H⁺) present in a solution.

The pH scale helps us determine whether a solution is acidic, basic, or neutral. It has numerous applications in medicine, agriculture, industries, environmental science, and our daily lives.

What is the pH Scale?

The pH scale is a numerical scale ranging from 0 to 14.

• pH = 7 → Neutral
• pH less than 7 → Acidic
• pH greater than 7 → Basic (Alkaline)

The lower the pH value, the stronger the acid.

The higher the pH value, the stronger the base.

pH Scale Chart

Universal Indicator

A universal indicator is a mixture of several indicators that produces different colours at different pH values.

It provides a more accurate estimate of pH than litmus paper.

Colour Changes of Universal Indicator

Importance of pH in Everyday Life

The concept of pH is closely connected with many biological and environmental processes.

1. pH in Our Digestive System

Our stomach produces hydrochloric acid (HCl) to help digest food and destroy harmful microorganisms.

Sometimes, excess acid is produced, leading to indigestion or acidity.

How is Acidity Controlled?

Doctors recommend antacids, which are mild bases.

Common antacids include:

• Magnesium hydroxide (Milk of Magnesia)
• Sodium hydrogen carbonate

These neutralise excess stomach acid and provide relief.

2. pH and Tooth Decay

The normal pH of our mouth is around 6.5 to 7.5.

When we consume sugary foods, bacteria present in the mouth produce acids.

If the pH falls below 5.5, the enamel of the teeth begins to dissolve, leading to tooth decay.

Prevention

• Brush your teeth twice a day.
• Avoid excessive sugary foods.
• Use toothpaste, which is generally basic and helps neutralise acids.

3. pH of Soil

Plants require a suitable soil pH for healthy growth.

Most crops grow well in slightly acidic to neutral soil (pH 6.5–7.5).

If Soil is Too Acidic

Farmers add:

• Quick lime (CaO)
• Slaked lime [Ca(OH)₂]

These substances increase the soil pH.

If Soil is Too Basic

Organic manure or compost is added to lower the pH gradually.

4. Self-Defence by Plants and Animals

Many plants and animals use acids or bases as a defence mechanism.

Ant Bite

Ants inject formic acid, causing pain and irritation.

Applying baking soda paste or calamine lotion helps neutralise the acid.

Bee Sting

Bee stings are also acidic in nature.

A mild base such as baking soda can help reduce discomfort.

Wasp Sting

Some wasp stings are alkaline (basic).

Applying a weak acid such as vinegar may help neutralise the sting.

5. Acid Rain

Acid rain forms when sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) react with water vapour in the atmosphere.

Harmful Effects

• Damages crops
• Corrodes buildings and monuments
• Pollutes lakes and rivers
• Harms aquatic life

Reducing industrial pollution and vehicle emissions helps control acid rain.

Common Salts

Salts are ionic compounds generally formed during neutralisation reactions.

Many salts are useful in everyday life.

Some important salts included in the CBSE syllabus are:

• Sodium Chloride
• Baking Soda
• Washing Soda
• Bleaching Powder
• Plaster of Paris

1. Sodium Chloride (Common Salt)

Chemical Formula

NaCl

Preparation

Produced by the reaction:

HCl + NaOH → NaCl + H₂O

Uses

• Cooking
• Food preservation
• Manufacture of chemicals
• Preparation of sodium hydroxide

2. Baking Soda

Chemical Name

Sodium Hydrogen Carbonate

Chemical Formula

NaHCO₃

Preparation

Baking soda is prepared by the Solvay Process.

Properties

• White crystalline powder
• Mildly basic
• Soluble in water

Uses

• Baking cakes and bread
• Fire extinguishers
• Antacid
• Soda-acid fire extinguishers

Heating Baking Soda

When heated,

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

Carbon dioxide released makes cakes and bread soft and fluffy.

3. Washing Soda

Chemical Name

Sodium Carbonate Decahydrate

Chemical Formula

Na₂CO₃·10H₂O

Preparation

Heating baking soda produces sodium carbonate.

Adding water forms washing soda crystals.

Uses

• Softening hard water
• Cleaning agent
• Glass industry
• Soap industry
• Paper industry

4. Bleaching Powder

Chemical Formula

CaOCl₂

Preparation

Prepared by passing chlorine gas over dry slaked lime.

Uses

• Disinfecting drinking water
• Bleaching cotton and linen
• Textile industry
• Paper industry
• Swimming pools

5. Plaster of Paris (POP)

Chemical Name

Calcium Sulphate Hemihydrate

Chemical Formula

CaSO₄·½H₂O

Preparation

Obtained by heating gypsum.

CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O

Properties

• White powder
• Sets into a hard mass when mixed with water
• Easy to mould

Uses

• Orthopaedic casts
• Decorative items
• Statues
• False ceilings
• Toys
• Chalks

Water of Crystallisation

Some salts contain a fixed number of water molecules within their crystal structure.

This water is called water of crystallisation.

Definition

Water of crystallisation is the fixed number of water molecules chemically bound to one formula unit of a salt.

Examples

Why is Water of Crystallisation Important?

It:

• Maintains the crystal structure.
• Gives the salt its characteristic colour.
• Affects the physical properties of salts.

Important Chemical Equations

Formation of Common Salt

HCl + NaOH → NaCl + H₂O

Heating Baking Soda

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

Formation of Plaster of Paris

CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O

Did You Know?

The Taj Mahal is affected by acid rain, which gradually damages its marble surface. Environmental protection measures are important to preserve such historical monuments.

Exam Tip

Remember the chemical names, formulae, preparation methods, and uses of Baking Soda, Washing Soda, Bleaching Powder, and Plaster of Paris. Questions based on these compounds appear regularly in CBSE board examinations.

Quick Revision

• The pH scale ranges from 0 to 14.
• pH 7 is neutral.
• Acids have pH below 7.
• Bases have pH above 7.
• Universal indicator shows different colours for different pH values.
• Tooth enamel begins to dissolve when the mouth’s pH falls below 5.5.
• Antacids neutralise excess stomach acid.
• Baking soda is NaHCO₃.
• Washing soda is Na₂CO₃·10H₂O.
• Bleaching powder is CaOCl₂.
• Plaster of Paris is CaSO₄·½H₂O.
• Water of crystallisation is chemically bound water present in certain salts.

Chapter Summary, Important Definitions, FAQs & Board Exam Preparation

Congratulations! You have completed Chapter 2 – Acids, Bases and Salts. This final section will help you revise the entire chapter quickly and prepare effectively for the CBSE Board Examination.

Important Definitions

Acid

A substance that releases hydrogen ions (H⁺) when dissolved in water.

Base

A substance that releases hydroxide ions (OH⁻) when dissolved in water.

Alkali

A base that is soluble in water.

Examples: Sodium hydroxide (NaOH), Potassium hydroxide (KOH)

Salt

An ionic compound formed when an acid reacts with a base during a neutralisation reaction.

Indicator

A substance that changes colour (or smell) to indicate whether a solution is acidic or basic.

Universal Indicator

A mixture of indicators that shows different colours over a wide range of pH values.

Neutralisation

A chemical reaction between an acid and a base to produce salt and water.

pH Scale

A numerical scale from 0 to 14 used to measure the acidity or basicity of a solution.

Water of Crystallisation

The fixed number of water molecules chemically combined with one formula unit of a crystalline salt.

NCERT Keywords

• Acid
• Base
• Alkali
• Salt
• Indicator
• Litmus
• Turmeric
• China Rose Indicator
• Phenolphthalein
• Methyl Orange
• Olfactory Indicator
• Universal Indicator
• pH Scale
• Neutralisation
• Water of Crystallisation
• Baking Soda
• Washing Soda
• Bleaching Powder
• Plaster of Paris
• Gypsum

Important Chemical Formulae

Important Chemical Equations

Acid + Metal

Zn + 2HCl → ZnCl₂ + H₂↑

Acid + Metal Carbonate

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑

Acid + Metal Bicarbonate

NaHCO₃ + HCl → NaCl + H₂O + CO₂↑

Acid + Base (Neutralisation)

HCl + NaOH → NaCl + H₂O

Heating Baking Soda

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

Formation of Plaster of Paris

CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O

Important Differences

Difference Between Acids and Bases

Difference Between Strong and Weak Acids

Difference Between Strong and Weak Bases

One-Page Quick Revision

✅ Acids release H⁺ ions.

✅ Bases release OH⁻ ions.

✅ Acids turn blue litmus red.

✅ Bases turn red litmus blue.

✅ Neutralisation produces salt + water.

✅ pH less than 7 indicates an acid.

✅ pH greater than 7 indicates a base.

✅ pH 7 is neutral.

✅ Tooth enamel starts dissolving below pH 5.5.

✅ Antacids neutralise excess stomach acid.

✅ Baking Soda = NaHCO₃

✅ Washing Soda = Na₂CO₃·10H₂O

✅ Bleaching Powder = CaOCl₂

✅ Plaster of Paris = CaSO₄·½H₂O

Frequently Asked Questions (FAQs)

1. What is an acid?

An acid is a substance that releases hydrogen ions (H⁺) in an aqueous solution.

2. What is a base?

A base is a substance that releases hydroxide ions (OH⁻) in water.

3. What is an alkali?

An alkali is a water-soluble base.

4. What is the pH of a neutral solution?

A neutral solution has a pH of 7.

5. Why does tooth decay occur?

Tooth decay occurs when bacteria produce acids that lower the pH in the mouth below 5.5, causing the enamel to dissolve.

6. Why are antacids used?

Antacids are mild bases that neutralise excess hydrochloric acid in the stomach and relieve acidity.

7. Why is baking soda used in cakes?

When heated, baking soda releases carbon dioxide gas, making cakes and bread soft and fluffy.

8. What is water of crystallisation?

It is the fixed number of water molecules chemically attached to one formula unit of a crystalline salt.

9. What is the chemical formula of Plaster of Paris?

CaSO₄·½H₂O

10. Name two natural indicators.

• Litmus
• Turmeric

Board Exam Tips

Most Important Topics

⭐ Properties of acids and bases

⭐ Indicators and their colour changes

⭐ Reactions of acids and bases

⭐ pH scale

⭐ Importance of pH in everyday life

⭐ Common salts

⭐ Water of crystallisation

⭐ Chemical equations

Frequently Asked Board Questions

• Define acids, bases, and salts.
• Explain neutralisation with an example.
• Draw the pH scale.
• Why does tooth decay occur below pH 5.5?
• Write the preparation and uses of baking soda.
• Differentiate between strong and weak acids.
• Explain water of crystallisation with examples.
• Give the chemical formulae of important compounds.

Chapter Summary

In this chapter, you learned that acids, bases, and salts are essential substances used in daily life, laboratories, and industries. You studied their properties, indicators used to identify them, and their reactions with different substances. The concept of the pH scale explained how the strength of acids and bases is measured and why maintaining the correct pH is important for human health, agriculture, and the environment.

The chapter also introduced important salts such as baking soda, washing soda, bleaching powder, and plaster of Paris, along with their preparation, properties, and practical applications. These concepts form the foundation for understanding many chemical processes and are highly relevant for CBSE board examinations.

💡 Did You Know?

The pH of human blood is maintained between 7.35 and 7.45. Even a small change in this range can seriously affect the normal functioning of the body, which is why maintaining pH balance is essential for good health.

📘 Prepare Smarter with the Complete CBSE Class 10 Science Master Guide

These free notes provide a strong conceptual foundation. For complete board exam preparation, explore the CBSE Class 10 Science Master Guide by Science World By Tushar Sir.

The Complete Guide Includes:

✅ Detailed Theory with Easy Explanations

✅ Mind Maps for Every Chapter

✅ NCERT-Based Notes

✅ Chapter-wise MCQs

✅ Assertion & Reason Questions

✅ Case-Based Questions

✅ Chapter Tests

✅ Smart Revision Notes

📖 Available in Two Formats

📕 Paperback Edition – Ideal for classroom study and revision.

📱 eBook Edition – Learn anytime, anywhere on your mobile, tablet, or computer.

Science World By Tushar Sir

Learn Smart • Practice Well • Score High

Continue Your Learning

Previous Chapter: Chemical Reactions and Equations

Next Chapter: Metals and Non-Metals