Chemistry Class 11 NCERT Solutions: Chapter 12 Organic Chemistry Some Basic Principles and Techniques Part 16

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Q: 37. In the Lassaigne’s test for nitrogen in an organic compound, the Prussian blue colour is obtained due to the formation of:

(A)

(B)

(C)

(D)

Answer:

In the Lassaigne’s test for nitrogen in an organic compound, the sodium fusion extract is boiled with iron (II) sulphate and then acidified with sulphuric acid. In the process, sodium cyanide first reacts with iron (II) sulphate and forms sodium hexacyanoferrate (II). Then, on heating with sulphuric acid, some iron (II) gets oxidised to form iron (III) hexacyanoferrate (II), which is Prussian blue in colour. The chemical equations involved in the reaction can be represented as

Hence, the Prussian blue colour is due to the formation of .

Q: 38. Which of the following carbocation is most stable?

(A)

(B)

(C)

(D)

Answer:

is a tertiary carbocation. A tertiary carbocation is the most stable carbocation due to the electron releasing effect of three methyl groups. An increased effect by three methyl groups stabilizes the positive charge on the carbocation.

Q: 39. The best and latest technique for isolation, purification and separation of organic compounds is:

(A) Crystallisation

(B) Distillation

(C) Sublimation

(D) Chromatography

Answer:

Chromatography is the most useful and the latest technique of separation and purification of organic compounds. It was first used to separate a mixture of coloured substances.

Q: 40. The reaction

Is classified as:

(A) Electrophilic substitution

(B) Nucleophilic Substitution

(C) Elimination

(D) Addition

Answer:

It is an example of nucleophilic substitution reaction. The hydroxyl group of with a lone pair of itself acts as a nucleophile and substitutes iodide ion in to form ethanol.

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