Homologous Series MCQs Quiz | Class 10
Test your understanding of Class X Science (Code 086), Unit I: Chemical Substances – Nature and Behaviour. This quiz covers the definition of homologous series, general formulas, the CH2 difference between successive members, and trends in physical and chemical properties. Click ‘Submit Quiz’ to check your score and download the answer PDF.
Homologous Series: Key Concepts
A homologous series is a family of organic compounds that have the same general formula and similar chemical properties because they contain the same functional group. The successive members of the series differ by a -CH2- unit or 14 atomic mass units (u).
1. Characteristics of a Homologous Series
- General Formula: All members can be represented by the same general formula (e.g., Alkanes: CnH2n+2).
- Functional Group: They contain the same functional group, which determines their chemical properties.
- Successive Difference: Any two consecutive members differ by one carbon atom and two hydrogen atoms (-CH2-).
- Mass Difference: The molecular mass of consecutive members differs by 14 u.
- Chemical Properties: Since the functional group is the same, the chemical reactions are very similar.
- Physical Properties: There is a gradual change (gradation) in physical properties like melting point, boiling point, and density as the molecular mass increases. For example, boiling points increase with increasing molecular mass.
2. Common Homologous Series
| Series Name | General Formula | First Member | Suffix |
|---|---|---|---|
| Alkanes | CnH2n+2 | Methane (CH4) | -ane |
| Alkenes | CnH2n | Ethene (C2H4) | -ene |
| Alkynes | CnH2n-2 | Ethyne (C2H2) | -yne |
| Alcohols | CnH2n+1OH | Methanol (CH3OH) | -ol |
3. Quick Revision Points
- Methane (CH4) and Ethane (C2H6) are homologues.
- Methanol (CH3OH) and Ethanol (C2H5OH) belong to the alcohol series.
- Solubility in water generally decreases as the carbon chain length increases for alcohols.
- Higher molecular mass leads to stronger Van der Waals forces, resulting in higher boiling points.
4. Extra Practice Questions
- Write the formula of the next homologue of Butane (C4H10). (Answer: Pentane, C5H12)
- Which functional group is present in the homologous series of carboxylic acids? (Answer: -COOH)
- If an alkene has 10 carbon atoms, how many hydrogen atoms does it have? (Answer: 20, Formula C10H20)
- Why do isomers not form a homologous series? (Answer: Isomers have the same molecular formula but different structures, whereas homologues have different molecular formulas.)
- Does the melting point increase or decrease as we go down a homologous series? (Answer: Increases)
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