Homologous Series - UNSOLVED PRACTICE SET
Chapter: Carbon and Its Compounds | Topic: Homologous Series
HOMOLOGOUS SERIES - UNSOLVED PRACTICE SET
Topic: Homologous Series
Multiple Choice Questions
Q1. Which of the following is a characteristic of a homologous series?
- Members have different functional groups
- Successive members differ by a —CH₂— group
- Members show different chemical properties
- Members have no regular pattern in physical properties
Q2. The general formula CₙH₂ₙ₊₂ represents:
- Alkenes
- Alkynes
- Alkanes
- Alcohols
Q3. Which of the following pairs belong to the same homologous series?
- Methane and Ethene
- Ethanol and Propanol
- Ethanoic acid and Propanone
- Methanal and Ethanol
Q4. The difference in molecular mass between two successive members of a homologous series is:
- 12 u
- 14 u
- 16 u
- 18 u
Q5. Which property does NOT show a regular trend in a homologous series?
- Melting point
- Boiling point
- Chemical properties
- Physical state
Q6. The first member of the alkyne series is:
- Methane
- Ethene
- Ethyne
- Propyne
Short Answer Questions
Q7. Define a homologous series. List any two characteristics of members of a homologous series.
Q8. Write the next two members of the following homologous series:
(a) Methane (CH₄), Ethane (C₂H₆), ...
(b) Methanol (CH₃OH), Ethanol (C₂H₅OH), ...
Q9. Why do members of a homologous series show similar chemical properties but gradually changing physical properties?
Q10. Arrange the following in increasing order of their boiling points: methane, ethane, propane, butane. Give a reason for your answer.
Q11. Your father uses kerosene (a mixture of C₁₀-C₁₆ hydrocarbons) in a lamp and petrol (C₅-C₁₂ hydrocarbons) in his car. Both belong to the same homologous series. Why does kerosene have a higher boiling point than petrol?
Q12. Write the molecular formulae of the first three members of the carboxylic acid homologous series.
Long Answer Questions
Q13. Explain what is meant by a homologous series with a suitable example. Describe the following characteristics of a homologous series:
(a) Same functional group
(b) Gradual change in physical properties
(c) Similar chemical properties
(d) Difference of CH₂ between successive members
Q14. Write the names, molecular formulae, and structural formulae of the first four members of the alkane series. Show how each successive member differs from the previous one by a —CH₂— group. Calculate the difference in molecular mass between methane and butane.
Q15. During a class discussion, your teacher explains that cooking gas (LPG) contains propane and butane, while petrol contains pentane, hexane, and heptane. All these belong to the same homologous series.
(a) Name the homologous series.
(b) Why is propane used as cooking gas and not pentane?
(c) Explain why all these compounds burn with a blue flame when sufficient air is available.
(d) What happens to the physical state as the number of carbon atoms increases from 3 to 7?
Numerical / Application-Based Problems
Q16. The molecular mass of the first member of an alcohol homologous series is 32 u.
(a) Identify the compound and write its molecular formula.
(b) Write the molecular formula of the third member of this series.
(c) Calculate the difference in molecular mass between the first and third members.
Q17. A homologous series has the general formula CₙH₂ₙ₊₁OH.
(a) Name the homologous series.
(b) Write the structural formula of the member where n = 2.
(c) If the molecular mass of a member is 60 u, find the value of n.
(Atomic masses: C = 12, H = 1, O = 16)
Q18. The following table shows some members of a homologous series:
Table
Compound Molecular Formula Boiling Point (°C)
A CH₄ -162
B C₂H₆ -89
C C₃H₈ -42
D C₄H₁₀ -0.5
(a) Name the homologous series.
(b) Predict the boiling point of C₅H₁₂. Give a reason.
(c) Which compound would be a gas at room temperature (25°C)? Explain.
(d) Calculate the molecular mass of compound D.