Class 10 Science Chapter 4

Hydrocarbons

Hydrocarbons are compounds made up of only carbon and hydrogen atoms.

They are the simplest organic compounds and form the basis of organic chemistry.

Examples

• Methane (CH₄)
• Ethane (C₂H₆)
• Propane (C₃H₈)
• Butane (C₄H₁₀)

Types of Hydrocarbons

1. Saturated Hydrocarbons (Alkanes)

These hydrocarbons contain only single bonds between carbon atoms.

• Example: Methane (CH₄), Ethane (C₂H₆)
• General formula → CₙH₂ₙ₊₂

2. Unsaturated Hydrocarbons

These hydrocarbons contain double or triple bonds.

(a) Alkenes

• Contain double bond
• General formula → CₙH₂ₙ

(b) Alkynes

• Contain triple bond
• General formula → CₙH₂ₙ₋₂

Structure of Hydrocarbons

Carbon atoms can form different types of structures:

• Straight chain → CH₃-CH₂-CH₃
• Branched chain → CH₃-CH(CH₃)-CH₃
• Ring structure → Cyclohexane

This is possible due to catenation property of carbon.

Homologous Series

A homologous series is a group of organic compounds having similar chemical properties and same functional group.

Characteristics

• Same general formula
• Same functional group
• Successive members differ by CH₂ group
• Gradual change in physical properties

Example

• CH₄ (Methane)
• C₂H₆ (Ethane)
• C₃H₈ (Propane)
• C₄H₁₀ (Butane)

Nomenclature of Carbon Compounds

Naming of carbon compounds is done using IUPAC system.

Rules

• Count number of carbon atoms
• Identify functional group
• Use proper suffix and prefix

Examples

• CH₄ → Methane
• C₂H₆ → Ethane
• C₃H₈ → Propane
• C₄H₁₀ → Butane

Functional Groups

Functional groups are specific groups of atoms present in a molecule which determine its chemical properties.

They replace one or more hydrogen atoms in a hydrocarbon.

Important Functional Groups

Homologous Series (Functional Group Based)

Compounds having same functional group form a homologous series.

Example: Alcohol Series

• CH₃OH (Methanol)
• C₂H₅OH (Ethanol)
• C₃H₇OH (Propanol)

Each successive member differs by CH₂ group.

Chemical Reactions of Carbon Compounds

Carbon compounds undergo various chemical reactions. These reactions are very important for exams.

1. Combustion Reaction

Carbon compounds burn in air (oxygen) to produce carbon dioxide and water along with heat and light.

Important Points

• Produces heat → used as fuel
• Complete combustion → blue flame
• Incomplete combustion → yellow flame (sooty)

2. Oxidation Reaction

Oxidation is the addition of oxygen or removal of hydrogen.

Ethanol is oxidised to ethanoic acid using oxidising agents.

• Oxidising agents: KMnO₄, K₂Cr₂O₇

3. Addition Reaction

Unsaturated hydrocarbons undergo addition reactions.

Hydrogen is added in presence of catalyst like nickel or palladium.

• Used in hydrogenation of oils
• Converts vegetable oil into ghee

4. Substitution Reaction

In this reaction, one atom is replaced by another atom.

Occurs in saturated hydrocarbons.

Important Concepts

• Combustion reaction produces heat
• Oxidation converts alcohol into acid
• Addition reaction occurs in unsaturated compounds
• Substitution reaction occurs in saturated compounds

These reactions are very important for board exams.

Ethanol

Ethanol is an alcohol with chemical formula C₂H₅OH. It is one of the most commonly used organic compounds.

Preparation of Ethanol

Ethanol is prepared by fermentation of sugars.

Properties of Ethanol

• Colorless liquid
• Has pleasant smell
• Boiling point → 78°C
• Miscible with water

Chemical Properties of Ethanol

1. Reaction with Sodium

2. Oxidation

3. Dehydration

This reaction takes place in presence of concentrated sulphuric acid.

Uses of Ethanol

• Used as fuel
• Used in medicines
• Used as solvent

Ethanoic Acid (Acetic Acid)

Ethanoic acid has chemical formula CH₃COOH. It is a weak acid commonly known as acetic acid.

Properties

• Sour taste
• Freezes at 16.6°C (glacial acetic acid)
• Soluble in water

Chemical Reactions

1. Reaction with Metals

2. Reaction with Bases

3. Reaction with Carbonates

Uses of Ethanoic Acid

• Used in vinegar
• Used as preservative
• Used in chemical industries

Esterification Reaction

When alcohol reacts with acid, it forms ester and water.

Ester has a sweet smell.

Uses

• Used in perfumes
• Used in flavoring agents

Saponification Reaction

Ester reacts with alkali to form alcohol and soap.

This process is used in making soap.

Soaps

Soaps are sodium or potassium salts of long-chain fatty acids.

Properties

• Used for cleaning
• Form lather in soft water
• Do not work well in hard water

Micelle Formation

Soap molecules form structures called micelles.

• Hydrophobic tail → attracts dirt
• Hydrophilic head → attracts water

Detergents

Detergents are synthetic cleaning agents.

Advantages

• Work in hard water
• More effective than soap

Disadvantages

• Non-biodegradable
• Cause water pollution

Final Summary of Chapter 4

• Carbon forms covalent bonds
• Hydrocarbons are basic compounds
• Functional groups define properties
• Ethanol is alcohol
• Ethanoic acid is weak acid
• Soaps are cleaning agents
• Detergents work in hard water

This chapter is very important for exams and practical life.

All Important Chemical Equations (Carbon and its Compounds)

This section contains all important chemical equations of Chapter 4 for quick revision.

1. Combustion Reactions

2. Oxidation Reactions

Oxidising agents: KMnO₄, K₂Cr₂O₇

3. Addition Reactions

Hydrogenation in presence of Ni/Pd catalyst

4. Substitution Reactions

5. Ethanol Reactions

Fermentation

Reaction with Sodium

Oxidation

Dehydration

6. Ethanoic Acid Reactions

With Metals

With Bases

With Carbonates

7. Esterification Reaction

8. Saponification Reaction

Final Equation Summary

• Combustion → CO₂ + H₂O + Heat
• Oxidation → Alcohol → Acid
• Addition → Unsaturated → Saturated
• Substitution → Replacement reaction
• Esterification → Ester + Water
• Saponification → Soap formation