Class 11 Chemistry NCERT Solutions For Chapter 12 Organic Chemistry – Some Basic Principles and Techniques

Chapter 12 Organic Chemistry – Some Basic Principles And Techniques

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NCERT Solutions Exercises Questions

Question 12.1 What are hybridisation states of each carbon atom in the following compounds ? CH2=C=O, CH3CH=CH2, (CH3)2CO, CH2=CHCN, C6H6

Question 12.2 Indicate the σ and π bonds in the following molecules : C6H6, C6H12, CH2Cl2, CH2=C=CH2, CH3NO2, HCONHCH3

Question 12.3 Write bond line formulas for : Isopropyl alcohol, 2,3-Dimethyl butanal, Heptan-4- one.

Question 12.4 Give the IUPAC names of the following compounds :

Question 12.5 Which of the following represents the correct IUPAC name for the compounds concerned ?
(a) 2,2-Dimethylpentane or 2-Dimethylpentane
(b) 2,4,7- Trimethyloctane or 2,5,7-Trimethyloctane
(c) 2-Chloro-4-methylpentane or 4-Chloro-2-methylpentane
(d) But-3-yn-1-ol or But-4-ol-1-yne.

Question 12.6 Draw formulas for the first five members of each homologous series beginning with the following compounds
(a) H–COOH
(b) CH3COCH3
(c) H–CH=CH2

Question 12.7Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for :
(a) 2,2,4-Trimethylpentane
(b) 2-Hydroxy-1,2,3-propanetricarboxylic acid
(c) Hexanedial

Question 12.8 Identify the functional groups in the following compounds

Question 12.9 Which of the two: O2NCH2CH2O– or CH3CH2O– is expected to be more stable and why ?

Question 12.10 Explain why alkyl groups act as electron donors when attached to a π system.

Question 12.11 Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation.
(a) C6H5OH
(b) C6H5NO2
(c) CH3CH=CHCHO
(d) C6H5–CHO
(e) 6 5 2 C H CH + −
(f) 3 2 CH CH CHCH + =

Question 12.12 What are electrophiles and nucleophiles ? Explain with examples.

Question 12.13Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles :
(a) 3 3 2 CH COOH + HO– → CH COO− + H O
(b) ( ) ( )( ) 3 3 3 2 CH COCH + → CH C CN OH – CN
(c) 6 5 6 5 3 C H + → C H COCH + 3 CH CO

Question 12.14 Classify the following reactions in one of the reaction type studied in this unit.
(a) 3 2 3 2 CH CH Br + HS− → CH CH SH
(b) ( ) ( ) 3 2 2 3 2 CH C = CH + HCl → CH ClC −
(c) 3 2 2 2 2 CH CH Br + HO− → CH = CH + H O
(d) ( ) ( ) 3 3 2 3 2 2 CH C − CH OH + HBr → CH CBrCH CH

Question 12.15 What is the relationship between the members of following pairs of structures ? Are they structural or geometrical isomers or resonance contributors ?

Question 12.16 For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion.

Question 12.17 Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids?
(a) Cl3CCOOH > Cl2CHCOOH > ClCH2COOH
(b) CH3CH2COOH > (CH3)2CHCOOH > (CH3)3C.COOH

Question 12.18 Give a brief description of the principles of the following techniques taking an example in each case.
(a) Crystallisation
(b) Distillation
(c) Chromatography

Question 12.19 Describe the method, which can be used to separate two compounds with different solubilities in a solvent S.

Question 12.20 What is the difference between distillation, distillation under reduced pressure and steam distillation ?

Question 12.21 Discuss the chemistry of Lassaigne’s test 12.22 Differentiate between the principle of estimation of nitrogen in an organic compound by (i) Dumas method and (ii) Kjeldahl’s method.

Question 12.23 Discuss the principle of estimation of halogens, sulphur and phosphorus present in an organic compound.

Question 12.24 Explain the principle of paper chromatography.

Question 12.25 Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?

Question 12.26 Explain the reason for the fusion of an organic compound with metallic sodium for testing nitrogen, sulphur and halogens.

Question 12.27 Name a suitable technique of separation of the components from a mixture of calcium sulphate and camphor.

Question 12.28 Explain, why an organic liquid vaporises at a temperature below its boiling point in its steam distillation ?

Question 12.29 Will CCl4 give white precipitate of AgCl on heating it with silver nitrate? Give reason for your answer.

Question 12.30 Why is a solution of potassium hydroxide used to absorb carbon dioxide evolved during the estimation of carbon present in an organic compound?

Question 12.31 Why is it necessary to use acetic acid and not sulphuric acid for acidification of sodium extract for testing sulphur by lead acetate test?

Question 12.32 An organic compound contains 69% carbon and 4.8% hydrogen, the remainder being oxygen. Calculate the masses of carbon dioxide and water produced when 0.20 g of this substance is subjected to complete combustion.

Question 12.33 A sample of 0.50 g of an organic compound was treated according to Kjeldahl’s method. The ammonia evolved was absorbed in 50 ml of 0.5 M H2SO4. The residual acid required 60 mL of 0.5 M solution of NaOH for neutralisation. Find the percentage composition of nitrogen in the compound.

Question 12.34 0.3780 g of an organic chloro compound gave 0.5740 g of silver chloride in Carius estimation. Calculate the percentage of chlorine present in the compound.

Question 12.35 In the estimation of sulphur by Carius method, 0.468 g of an organic sulphur compound afforded 0.668 g of barium sulphate. Find out the percentage of sulphur in the given compound.

Question 12.36 In the organic compound CH2 = CH – CH2 – CH2 – C ≡ CH, the pair of hydridised orbitals involved in the formation of: C2 – C3 bond is:
(a) sp – sp2
(b) sp – sp3
(c) sp2 – sp3
(d) sp3 – sp3

Question 12.37 In the Lassaigne’s test for nitrogen in an organic compound, the Prussian blue colour is obtained due to the formation of:
(a) Na4[Fe(CN)6]
(b) Fe4[Fe(CN)6]3
(c) Fe2[Fe(CN)6]
(d) Fe3[Fe(CN)6]4

Question 12.38 Which of the following carbocation is most stable ?
(a) (CH3)3C. +C H2
(b) (CH3)3 +C
(c) CH3CH2 +C H2
(d) CH3 +C H CH2CH3

Question 12.39The best and latest technique for isolation, purification and separation of organic compounds is:
(a) Crystallisation
(b) Distillation
(c) Sublimation
(d) Chromatography

Question 12.40The reaction: CH3CH2I + KOH(aq) → CH3CH2OH + KI is classified as :
(a) electrophilic substitution
(b) nucleophilic substitution
(c) elimination
(d) addition

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