CBSE Class 12 Chemistry Chapter 10: Haloalkanes and Haloarenes - NCERT Solutions
This resource provides comprehensive NCERT Solutions for Class 12 Chemistry, Chapter 10, focusing on Haloalkanes and Haloarenes. It addresses intext questions, guiding students through the nomenclature and structural representation of various halogenated organic compounds, including alkanes, cycloalkanes, and aromatic systems. The solutions explain the reactivity of alcohols with specific reagents like KI and sulfuric acid, highlighting why certain acids are preferred to prevent unwanted oxidation. It also details the different dihalogen derivatives of propane, illustrating their structures and nomenclature. These solutions are designed to clarify fundamental concepts and prepare students for their board examinations by offering step-by-step explanations and accurate chemical structures.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 12 |
| Subject | Chemiry |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | Chapter 10: Haloalkanes and Haloarenes - Intext Questions Solutions |
Chapter summary
This chapter's NCERT Solutions cover the intext questions for Haloalkanes and Haloarenes. It focuses on drawing structures of complex halogenated organic compounds based on IUPAC names, understanding the role of oxidizing agents in reactions involving alcohols and KI, and identifying all possible dihalogen derivatives of propane. The solutions provide clear structural representations and explanations for chemical principles.
Learning outcomes
- Understand the nomenclature and structure of haloalkanes and haloarenes.
- Draw the correct structures for given IUPAC names of halogenated hydrocarbons.
- Explain the reactivity of alcohols with KI and the role of sulfuric acid.
- Identify and draw different dihalogen derivatives of propane.
- Apply principles of organic chemistry to predict reaction outcomes.
Topics covered
Paper topics
- Nomenclature of Haloalkanes
- Structure of Haloalkanes
- Nomenclature of Haloarenes
- Structure of Haloarenes
- Reactions of Alcohols with KI
- Role of Sulfuric Acid in Reactions
- Oxidizing Agents
- Dihalogen Derivatives of Propane
- Isomerism in Dihalogenated Compounds
- Drawing Chemical Structures
Important topics
- Drawing structures from IUPAC names
- Reactions of alcohols with KI and H2SO4
- Identifying dihalogen derivatives
- Nomenclature of haloalkanes and haloarenes
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Questions and Solutions
(Chapter 10)(Heloakanes and Heloarenes) XII
Intext Questions
Question 10.1:
Write structures of the following compounds:
- 2-Chloro-3-methylpentane
- 1-Chloro-4-ethylcyclohexane
- 4-tert. Butyl-3-iodoheptane
- 1,4-Dibromobut-2-ene
- 1-Bromo-4-sec. butyl-2-methylbenzene
Answer (i) CH<sub>3</sub>
CH3-CH-CH-CH-CH3
- Chloro-3-methyl pentane
(ii)
C2H5
- Chloro-4-ethylcyclohexane
(iii)
CH3-CH2- <math>-\overset{31}{\text{CH}} - \overset{4}{\text{CH}} - \overset{5}{\text{CH}}_2 - \overset{6}{\text{CH}}_2 - \overset{7}{\text{CH}}_3</math> <math>CH_3 - C - CH_3</math>
CH3
- tert-Butyl-3-iodoheptane
(iv)
<math>Br - CH_2 - CH = CH_2 - CH_2 - Br</math>
1, 4-Dibromobut-2-ene
34
(v) CH3
<math>CH_3</math>—CH—<math>CH_2</math>—<math>CH_3</math>
- Bromo-4-sec-butyl-2-methylbenzene
Question 10.2:
Why is sulphuric acid not used during the reaction of alcohols with KI?
Answer
In the presence of sulphuric acid (H<sub>2</sub>SO<sub>4</sub>), KI produces HI
<math>2KI + H_2SO_4 \longrightarrow 2KHSO_4 + 2HI</math>
Since H<sub>2</sub>SO<sub>4</sub>
is an oxidizing agent, it oxidizes HI (produced in
the reaction to <math>I_2</math>).
<math>2HI + H_2SO_4 \longrightarrow I_2 + SO_2 + H_2O</math>
As a result, the reaction between alcohol and HI to produce alkyl iodide cannot occur. Therefore, sulphuric acid is not used during the reaction of alcohols with KI. Instead, a non-oxidizing acid such as H<sub>3</sub>PO<sub>4</sub> is used.
Question 10.3:
Write structures of different dihalogen derivatives of propane.
Answer
There are four different dihalogen derivatives of propane. The structures of these derivatives are shown below. (i) Br — CH — <math>CH_2</math> — <math>CH_3</math>
1, 1-Dibromopropane
35
Common mistakes
- Incorrectly drawing complex structures from IUPAC names.
- Misunderstanding the oxidizing nature of sulfuric acid in specific reactions.
- Failing to identify all possible isomers for dihalogen derivatives.
- Errors in representing chemical structures and bonding.
Revision tips
- Practice drawing structures for all given names repeatedly.
- Focus on the specific conditions and reagents mentioned in the questions, like the role of H2SO4 with KI.
- Systematically list and draw all isomers for compounds like dihalogenated propanes.
- Review the IUPAC naming conventions for haloalkanes and haloarenes.
Practice MCQs
Q1. Which acid is preferred over sulfuric acid when reacting alcohols with KI?
Explanation: Sulfuric acid is an oxidizing agent that oxidizes the HI produced, preventing the formation of alkyl iodide. Phosphoric acid is a non-oxidizing acid and is therefore preferred.
Q2. What is the product of the oxidation of HI by sulfuric acid?
Explanation: Concentrated sulfuric acid oxidizes hydrogen iodide (HI) to iodine (I2), along with sulfur dioxide and water.
Q3. How many dihalogen derivatives of propane are possible?
Explanation: There are four distinct dihalogen derivatives of propane, differing in the positions and types of halogen atoms attached.
Q4. In the compound 2-Chloro-3-methylpentane, where are the substituents located?
Explanation: The name indicates a five-carbon chain (pentane) with a chlorine atom on the second carbon and a methyl group on the third carbon.
Frequently asked questions
What is the main focus of the NCERT Solutions for Chapter 10: Haloalkanes and Haloarenes?
These solutions focus on understanding the structures, nomenclature, and basic reactions related to haloalkanes and haloarenes, specifically addressing the intext questions from the NCERT textbook.
Why is sulfuric acid avoided when alcohols react with KI?
Sulfuric acid is a strong oxidizing agent. It oxidizes the hydrogen iodide (HI) formed in the reaction to iodine (I2), thus preventing the formation of the desired alkyl iodide from the alcohol.
How can I correctly draw the structure for 4-tert. Butyl-3-iodoheptane?
Start by drawing a seven-carbon chain (heptane). Number the carbons from one end. Attach an iodine atom to the third carbon and a tert-butyl group to the fourth carbon. Ensure the tert-butyl group is correctly represented as -C(CH3)3.
What are the different dihalogen derivatives of propane?
The four different dihalogen derivatives of propane are 1,1-dibromopropane, 1,2-dibromopropane, 2,2-dibromopropane, and 1,3-dibromopropane (if considering bromine as the halogen).
How do these solutions help in exam preparation?
They provide clear, step-by-step explanations for each question, helping students understand the underlying chemical principles and practice drawing structures and predicting reaction outcomes, which are crucial for exams.
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