Organic chemistry guide for 10th class board exam Pakistan — hydrocarbons, functional groups, reactions, and naming rules explained clearly for SSC students.

Organic Chemistry for 10th Class — Complete Guide with Reactions

Quick Answer: Organic chemistry in 10th class covers carbon compounds — hydrocarbons (alkanes, alkenes, alkynes), functional groups (alcohols, carboxylic acids, aldehydes), and key reactions like combustion, addition, and substitution. Learn the naming rules (IUPAC) and practice identifying functional groups to score well in board exams.

Organic chemistry is the study of carbon-containing compounds. It might sound complex, but once you understand the pattern behind how organic compounds are named and how they react, the chapter becomes much more manageable. For 10th class board exams in Pakistan, organic chemistry is a predictable chapter — the same types of questions appear year after year.

This guide covers everything you need: naming rules, types of hydrocarbons, functional groups, and the key reactions that appear in board papers.

Why Carbon is Special — The Basis of Organic Chemistry

Before you can understand organic chemistry, you need to understand why carbon forms the backbone of all life and most of chemistry.

Carbon has four valence electrons, meaning it can form four covalent bonds. This gives carbon a unique ability: it can bond with itself repeatedly to form chains, rings, and branched structures. No other element does this as effectively. The result is millions of different organic compounds — from the simplest methane (CH₄) to the complex DNA in your cells.

In 10th class chemistry, you focus on the simplest carbon compounds: hydrocarbons (containing only carbon and hydrogen) and compounds with specific functional groups.

Homologous Series

A homologous series is a family of organic compounds that:

Have the same general formula
Differ from one another by a CH₂ unit
Have similar chemical properties
Show gradual change in physical properties

Examples: Alkanes (CₙH₂ₙ₊₂), Alkenes (CₙH₂ₙ), Alkynes (CₙH₂ₙ₋₂)

Hydrocarbons — Alkanes, Alkenes, and Alkynes

Hydrocarbons are the most fundamental organic compounds. Your board paper will almost certainly ask you to identify, name, or describe properties of hydrocarbons.

Alkanes (Saturated Hydrocarbons)

General Formula: CₙH₂ₙ₊₂

Alkanes contain only single bonds between carbon atoms. They are called saturated because they contain the maximum number of hydrogen atoms possible.

| Name | Formula | Structure | |------|---------|-----------| | Methane | CH₄ | 1 carbon | | Ethane | C₂H₆ | 2 carbons | | Propane | C₃H₈ | 3 carbons | | Butane | C₄H₁₀ | 4 carbons | | Pentane | C₅H₁₂ | 5 carbons |

Properties of Alkanes:

Non-polar, insoluble in water
Low boiling points (increase with molecular mass)
Undergo substitution reactions (not addition, because all bonds are single)

Key Reaction — Combustion: CH₄ + 2O₂ → CO₂ + 2H₂O (complete combustion, produces CO₂ and water) CH₄ + O₂ → CO + 2H₂O (incomplete combustion, produces CO — toxic carbon monoxide)

Substitution Reaction with Halogens: CH₄ + Cl₂ → CH₃Cl + HCl (in presence of UV light)

Alkenes (Unsaturated Hydrocarbons)

General Formula: CₙH₂ₙ

Alkenes contain one carbon-carbon double bond (C=C). They are unsaturated — they can accept more hydrogen.

| Name | Formula | |------|---------| | Ethene | C₂H₄ | | Propene | C₃H₆ | | Butene | C₄H₈ |

Key Reaction — Addition Reaction: Alkenes undergo addition reactions because of the double bond.

CH₂=CH₂ + H₂ → CH₃−CH₃ (Hydrogenation: alkene + hydrogen → alkane) CH₂=CH₂ + Br₂ → CH₂Br−CH₂Br (Bromination: decolorizes bromine water — test for unsaturation) CH₂=CH₂ + H₂O → CH₃−CH₂−OH (Hydration: makes ethanol)

Bromine Water Test: If a compound decolorizes orange bromine water, it is unsaturated (alkene or alkyne).

Alkynes (Unsaturated Hydrocarbons)

General Formula: CₙH₂ₙ₋₂

Alkynes contain one carbon-carbon triple bond (C≡C).

| Name | Formula | |------|---------| | Ethyne (Acetylene) | C₂H₂ | | Propyne | C₃H₄ |

Ethyne is important industrially — it burns with a very hot flame used in welding (oxyacetylene torch).

Functional Groups and Their Reactions

A functional group is an atom or group of atoms that gives an organic compound its characteristic chemical properties. Knowing functional groups lets you predict how a compound will react.

Alcohols (−OH group)

General Formula: CₙH₂ₙ₊₁OH (for primary alcohols)

| Name | Formula | |------|---------| | Methanol | CH₃OH | | Ethanol | C₂H₅OH | | Propanol | C₃H₇OH |

Properties:

Soluble in water (form hydrogen bonds)
React with sodium to produce hydrogen gas: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
Oxidised to aldehydes or carboxylic acids
Dehydration gives alkenes: C₂H₅OH → CH₂=CH₂ + H₂O (with H₂SO₄ catalyst)

Ethanol is the alcohol in beverages. Methanol is highly toxic — even small amounts cause blindness and death.

Carboxylic Acids (−COOH group)

General Formula: RCOOH

| Name | Formula | |------|---------| | Methanoic acid (formic acid) | HCOOH | | Ethanoic acid (acetic acid) | CH₃COOH |

Ethanoic acid (acetic acid) is the acid in vinegar.

Key Reactions:

React with metals to produce hydrogen: 2CH₃COOH + 2Na → 2CH₃COONa + H₂
React with carbonates: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
Esterification: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O (in presence of H₂SO₄ catalyst)

Esters (−COO− group)

Esters are formed when carboxylic acids react with alcohols. They have fruity smells and are used in perfumes and food flavourings.

IUPAC Naming Rules for Organic Compounds

The IUPAC (International Union of Pure and Applied Chemistry) system gives every organic compound a systematic name. Board exams regularly ask for IUPAC names.

Rules for Naming Alkanes

Find the longest carbon chain — this gives the parent name
Number carbons from the end closest to a branch
Name branches as substituents (methyl, ethyl, etc.)
Use numbers to show positions of branches

Prefixes for carbon chain length: 1C = meth-, 2C = eth-, 3C = prop-, 4C = but-, 5C = pent-

Suffix for each type:

Alkane: -ane
Alkene: -ene
Alkyne: -yne
Alcohol: -ol
Carboxylic acid: -oic acid

Example: A 3-carbon chain with an OH group at carbon 2 = propan-2-ol

This naming system is logical and consistent. Spend time practicing naming 10-15 structures before the exam.

Key Reactions Summary for Board Exam

Board examiners frequently ask students to complete reactions or identify reaction types. Here is a condensed reference:

| Reaction Type | Example | |--------------|---------| | Combustion (complete) | Alkane + O₂ → CO₂ + H₂O | | Combustion (incomplete) | Alkane + O₂ → CO + H₂O | | Addition (hydrogenation) | Alkene + H₂ → Alkane | | Addition (halogenation) | Alkene + X₂ → Dihalide | | Addition (hydration) | Alkene + H₂O → Alcohol | | Substitution | Alkane + X₂ → Haloalkane + HX | | Esterification | Acid + Alcohol ⇌ Ester + Water |

For board exams, you need to know the reactants, products, and conditions (catalyst, heat, light) for each reaction type.

After your board exam, check your chemistry result at /10th-class-result-2026 or view SSC Results for your board.

Frequently Asked Questions

Q: How much of the 10th class chemistry paper is organic chemistry? A: Typically 20-25% of the marks come from organic chemistry, depending on the BISE board. The chapter usually contributes to both short questions (Section B) and may appear in long questions (Section C).

Q: What is the difference between substitution and addition reactions? A: Substitution reactions replace one atom with another (alkanes + halogens). Addition reactions add atoms across a double bond (alkenes + H₂, Br₂, or H₂O). The key difference is that substitution requires single bonds (saturated) and addition requires double/triple bonds (unsaturated).

Q: How do I test if a compound is saturated or unsaturated? A: Add bromine water (orange/brown). If it decolorizes, the compound is unsaturated (contains double or triple bonds). This is a standard board exam practical question.

Q: What is esterification and why is it important? A: Esterification is the reaction of a carboxylic acid with an alcohol in the presence of an acid catalyst to form an ester and water. Esters are important because they give fruits their distinctive smells and are used in perfume and food industries.

Q: Do I need to draw structural formulas in the exam? A: Yes, some board questions ask for structural formulas, not just molecular formulas. Practice drawing the structures of methane, ethane, ethene, ethyne, ethanol, and ethanoic acid.

Q: What is the most important organic compound to know for the board exam? A: Ethanol (C₂H₅OH) appears most frequently — its properties, uses, reactions, and preparation are all common exam topics.