Vidaara.orgClass 10 · Chemistry
CodeVID-C10-04-T2-01
Assignment — Hydrocarbons, Functional Groups & Homologous Series
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The general formula of an alkene is:
- A.CnH2n+2
- B.CnH2n
- C.CnH2n-2
- D.CnHn
2.
The functional group present in ethanol is:
- A.−COOH
- B.−CHO
- C.−OH
- D.−CO−
3.
The first member of the alkyne series is:
- A.ethene
- B.ethyne
- C.methane
- D.propyne
4.
An unsaturated hydrocarbon burns with a flame that is:
- A.blue and clean
- B.yellow and sooty
- C.colourless
- D.green
5.
Compounds with the same molecular formula but different structures are called:
- A.allotropes
- B.homologues
- C.isomers
- D.isotopes
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Define a homologous series and state any one of its characteristics.
7.
What is a functional group? Name the functional group in CH3CHO.
8.
Differentiate between saturated and unsaturated hydrocarbons.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Draw and name the two structural isomers of pentane C5H12 that are straight and branched chains (any two).
10.
Write the names and formulae of the first three members of the alcohol homologous series.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Define a homologous series and list four characteristics. Illustrate with the first three alkanes, showing how their formulae and masses change.
Answer Key
Section A — Multiple Choice Questions
- (B) CnH2n
- (C) −OH
- (B) ethyne
- (B) yellow and sooty
- (C) isomers
Section B — Short Answer (2 marks)
- A homologous series is a family of compounds with the same functional group in which each member differs from the next by -CH2. One characteristic: members have the same general formula and similar chemical properties.
- A functional group is an atom or group of atoms that replaces a hydrogen and gives a compound its characteristic properties. In CH3CHO the functional group is the aldehyde group -CHO.
- Saturated hydrocarbons have only single carbon-carbon bonds (alkanes); unsaturated hydrocarbons have at least one double (alkene) or triple (alkyne) bond.
Section C — Short Answer (3 marks)
- n-Pentane: CH3-CH2-CH2-CH2-CH3 (straight chain). A branched isomer is isopentane (2-methylbutane): a four-carbon chain with a CH3 branch on the second carbon. (Neopentane, with two CH3 branches on a central carbon, is a third isomer.)
- Methanol CH3OH, ethanol C2H5OH and propanol C3H7OH; each differs from the next by a -CH2 unit.
Section D — Long Answer (5 marks)
- A homologous series is a group of compounds with the same functional group in which successive members differ by -CH2. Characteristics: (1) all members fit one general formula (alkanes CnH2n+2); (2) successive members differ by CH2 (14 u); (3) members have similar chemical properties; (4) physical properties (melting/boiling point) change gradually with increasing chain length. First three alkanes: methane CH4 (16 u), ethane C2H6 (30 u), propane C3H8 (44 u) - each is 14 u heavier than the previous, differing by one CH2 unit.
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