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Question
What is a homologous series? Explain with an example.
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Solution
- A group of compounds having similar structures and chemical properties but their successive compounds differ by a CH2 group is called a homologous series.
- Example: Alkanes have similar structures and similar chemical properties, so they can be grouped together to form a homologous series. The general formula of the homologous series of alkanes is CnH2n+2, where n is the number of carbon atoms in each molecule.
RELATED QUESTIONS
State any four characteristics of a homologous series
What is meant by homologous series of carbon compounds?
Write the name and formula of the 2nd member of homologous series having general formula CnH2n – 2.
Give the structural formula for 1, 2-dichloroethane
Fill in the following blank with suitable word:
Ethene and ethyne are examples of ..... hydrocarbons.
What is the next higher homologue of methanol (CH3OH)?
Write the names and formulae for the first three members of the homologous series for chloroalkanes.
The molecular formula of the third member of the homologous series of ketones is:
(a) C4H8O
(b) C3H6O
(c) C5H10O
(d) C6H12O
Succeeding members of a homologous series differ by ______.
What is the difference in the molecular formula of any two adjacent homologues in terms of molecular mass?
Study the different conclusions drawn by students of a class on the basis of observations of preserved/available specimens of plants and animals.
I. Potato and sweet potato are analogous organs in plants.
II. Wings of insects and wings of birds are homologous organs in animals.
III. Wings of insects and wings of bats are analogous organs in animals.
IV. Thorns of citrus and tendrils of cucurbita are analogous organs in plants.
The correct conclusions are:
(A) I, and II
(B) II and IV
(C) I and III
(D) III and IV
Give three points to differentiate between saturated and unsaturated
hydrocarbons.
Find the odd one out and give its explanation.
Complete the following table for the homologous series of alkanes.
| Name | Molecular formula | Condensed structural formula | Number of carbon atom | Number of -CH2- units | Boiling point °C |
| Methane | CH4 | CH4 | 1 | 1 | -162 |
| Ethane | C2H6 | CH3–CH3 | 2 | 2 | -88.5 |
| Propane | C3H8 | CH3–CH2–CH3 | 3 | 3 | -42 |
| Butane | C4H10 | CH3–CH2–CH2–CH3 | ______ | ______ | 0 |
| Pentane | C5H12 | CH3–CH2–CH2–CH2–CH3 | ______ | ______ | 36 |
| Hexane | C6H14 | CH3–CH2–CH2–CH2–CH2–CH3 | ______ | ______ | 69 |
Complete the following table for homologous series of alcohols.
| Name | Molecular formula | Condensed structural formula | Number of carbon atom | Number of -CH2- units | Boiling point °C |
| Methanol | CH4O | CH3-OH | 1 | 1 | 63 |
| Ethanol | C2H6O | CH3–CH2-OH | 2 | 2 | 78 |
| Propanol | C3H8O | CH3–CH2–CH2-OH | ______ | ______ | 97 |
| Butanol | C4H10O | CH3–CH2–CH2–CH2–OH | ______ | ______ | 118 |
Complete the following chart by using examples given in brackets.
(isobutylene, cyclohexane, propane, cyclohexene, cyclopentane, benzene, propyne, isobutane, propene)
| Straight chain hydrocarbons | Branched chain hydrocarbons | Cyclic hydrocarbons |
Which of the following does not belong to the same homologous series?
Study and complete the following table:
| Homologous series | Alkane | Alkyne |
| General formula | CnH2n+2 | 1. ______ |
| IUPAC name | 2. ______ | Ethyne |
| Common name | Marsh gas | 3. ______ |
Consider the following molecular formulae of carbon compounds:
(i) CH3COOH (ii) CH3OH (iii) C2H6 (iv) C3H4 (v) C4H8
- Which one of these compounds belongs to homologous series of alcohols?
- Identify the compound having triple bond between carbon-carbon atoms.
- Write the molecular formula of the first member of the homologous series to which CH3COOH belongs.
- Write the general formula of the series to which the compound C4H8 belongs.
Consider the carbon compounds having following molecular formula:
(i) C3H6 (ii) C3H8 (iii) C4H6 (iv) C6H6 (v) C6H12
- State the number of double covalent bonds present in C3H8.
- Write the formula of first member of the homologous series to which the carbon compound C4H6 belongs.
- Which one of the above compounds forms a ring structure of carbon atoms?
- Identify, which of the above compounds, is a member of alkane series.
