In short: Carbon and Its Compounds (Chapter 4) carries 4-5 marks in CBSE Class 10 Science. This chapter introduces organic chemistry — covalent bonding, homologous series, IUPAC nomenclature, and the properties of ethanol and ethanoic acid. It is the most conceptually different chapter in Chemistry because it deals with carbon's unique ability to form 4 bonds and create millions of compounds.
Why Carbon Is Special
Carbon has 4 valence electrons and forms covalent bonds (shared electron pairs). Two unique properties make carbon the basis of organic chemistry:
Catenation: Carbon can bond with other carbon atoms to form long chains, branched chains, and rings. No other element does this as effectively.
Tetravalency: Carbon forms 4 bonds, allowing complex structures.
Covalent Bonding
Unlike ionic compounds (NaCl), carbon compounds share electrons:
| Bond Type | Electrons Shared | Example |
|---|---|---|
| Single bond (—) | 2 electrons (1 pair) | CH₄ (methane) |
| Double bond (=) | 4 electrons (2 pairs) | C₂H₄ (ethene) |
| Triple bond (≡) | 6 electrons (3 pairs) | C₂H₂ (ethyne) |
Properties of covalent compounds:
- Low melting and boiling points
- Generally poor conductors of electricity
- Soluble in organic solvents (not always in water)
Homologous Series
A series of compounds with the same functional group and similar chemical properties, differing by -CH₂- unit.
Alkanes (CₙH₂ₙ₊₂) — Single bonds only
| Name | Formula | Structure |
|---|---|---|
| Methane | CH₄ | 1 carbon |
| Ethane | C₂H₆ | 2 carbons |
| Propane | C₃H₈ | 3 carbons |
| Butane | C₄H₁₀ | 4 carbons |
| Pentane | C₅H₁₂ | 5 carbons |
Alkenes (CₙH₂ₙ) — One double bond
Ethene (C₂H₄), Propene (C₃H₆), Butene (C₄H₈)
Alkynes (CₙH₂ₙ₋₂) — One triple bond
Ethyne (C₂H₂), Propyne (C₃H₄), Butyne (C₄H₆)
Board exam tip: Memorize the first 5 members of each series with their formulas. Know how to draw structural formulas.
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IUPAC Nomenclature
The IUPAC naming system follows a pattern: Prefix + Root + Suffix
| Carbon atoms | Root | Example (alkane) |
|---|---|---|
| 1 | Meth- | Methane |
| 2 | Eth- | Ethane |
| 3 | Prop- | Propane |
| 4 | But- | Butane |
| 5 | Pent- | Pentane |
Suffix by bond type:
- Single bond: -ane
- Double bond: -ene
- Triple bond: -yne
Functional group suffixes:
- Alcohol (-OH): -ol (e.g., Ethanol)
- Carboxylic acid (-COOH): -oic acid (e.g., Ethanoic acid)
- Aldehyde (-CHO): -al (e.g., Ethanal)
- Ketone (-CO-): -one (e.g., Propanone)
Ethanol (C₂H₅OH)
Properties:
- Liquid at room temperature
- Pleasant smell
- Miscible with water
- Used as solvent, fuel, in beverages
Important reactions:
1. Combustion: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + Heat
2. Oxidation (with alkaline KMnO₄ or acidified K₂Cr₂O₇): C₂H₅OH → CH₃COOH (ethanoic acid)
3. Dehydration (with conc. H₂SO₄ at 443K): C₂H₅OH → C₂H₄ + H₂O (ethene + water)
Ethanoic Acid (CH₃COOH)
Also called acetic acid. Vinegar is 5-8% acetic acid in water.
Properties:
- Sour taste, pungent smell
- Melting point: 290K (below this it freezes — called "glacial acetic acid")
Important reactions:
1. Esterification (with ethanol): CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O (ester + water)
2. Reaction with NaOH (neutralization): CH₃COOH + NaOH → CH₃COONa + H₂O
3. Reaction with Na₂CO₃: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
Soaps and Detergents
Soap: Sodium or potassium salt of long-chain carboxylic acid (fatty acid). Saponification: Ester + NaOH → Soap + Glycerol
Micelle formation: Soap molecules have a hydrophobic (water-hating) tail and a hydrophilic (water-loving) head. In water, they form clusters (micelles) that trap oil/grease.
Soap vs Detergent:
| Soap | Detergent |
|---|---|
| Made from natural fats/oils | Made from petrochemicals |
| Does not work in hard water (forms scum) | Works in hard water |
| Biodegradable | Some are non-biodegradable |
Board Exam Important Questions
- What is catenation? Why is carbon uniquely suited for it? (2-3 marks)
- Write the structural formula of ethanol and ethanoic acid. (2 marks)
- What happens when ethanol is heated with conc. H₂SO₄ at 443K? Write the equation. (2-3 marks)
- Explain the esterification reaction with an equation. (3 marks)
- What is a homologous series? Write the first 5 members of the alkane series. (3 marks)
- Explain how soap cleans clothes using the micelle concept. (3-5 marks)
- Differentiate between soaps and detergents. (2-3 marks)
- What is saponification? Give the equation. (2-3 marks)
For the complete marks distribution, see the CBSE Class 10 Science marks weightage. For all chemical equations, see the Science formulas list.
Frequently Asked Questions
How many marks does Carbon and Its Compounds carry?
4-5 marks in the CBSE Class 10 Science paper, as part of the 25-mark "Chemical Substances" unit.
Do I need to memorize structural formulas?
Yes. You should be able to draw the structural formula of methane, ethane, ethene, ethyne, ethanol, and ethanoic acid. These appear as MCQs and short-answer questions.
Is IUPAC naming important for the exam?
Moderately. You should know how to name alkanes, alkenes, and alkynes up to 5 carbons, and recognize functional groups (alcohol, carboxylic acid). Full IUPAC naming of complex molecules is not expected at Class 10 level.
What equations should I memorize?
Combustion of ethanol, oxidation of ethanol to ethanoic acid, dehydration of ethanol, esterification, and saponification. These 5 reactions cover most exam questions from this chapter.
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