Class 11 Chemistry Organic Chemistry Some Basic Principles and Techniques Exam Questions

LEVEL – 1

1. Suggest a method to purify a liquid which decomposes at its boiling point?

Ans: The process Distillation Under reduced pressure is used to purify aliquid which decomposes at its boiling point.

2. How will you separate a mixture of O-nitrophenol and P-nitrophenol?

Ans: O-nitrophenol is steam volatile therefore it can be separated by Steam distillation.

3. Lassaigne's test is not shown by diazonium salt .Why?

Ans: On heating diazoniumsalt , loses Nitrogen and could not fuse with the Sodium metal therefore diazonium salt does not show Positive Lassaigne's test for Nitrogen .

4. Why alcohols are weaker acids than Water?

Ans: The alkyl group in alcohol is has +I effect due to which electron density increases on oxygen atom which makes the release of H⁺ ion more difficult from alcohol R→ O – H

5. Why is nitric acid is added to Sodium Extract before adding Silvernitrate for testing halogens?

Ans: Nitric acid is added to decompose NaCN& Na₂ S .

NaCN + HNO_₃ → NaNO₃ + HCN

Na₂ S + HNO₃ → 2NaNO₃ + H₂ S

6. Write the hybridized state of C atoms in the following

Ans: (i) C-O is more polar because O is more electronegative than N

(ii) C-O is more polar because O is more electronegative than S

9. In which C-C bond of CH₃CH₂CH₂Br , the inductive effect is expected to be the least.

Ans: Magnitude of inductive effect diminishes as the intervening bonds increases. Hence, the effect is least in the bond between C-3 and C-2.

10. Why (CH₃)₃C⁺ carbocation is more easily formed than ( CH₃)₂C⁺H carbocation ?

Ans: Tertiary butyl carbocation is more stable than isopropyl carbocation.

11. Diphenylketone ( C₆H₅-CO-C₆H₅ ) shows tautomerism. Explain.

Ans: It contains two alpha H atoms.

12. What are Electrophiles and Nucleophiles?

Ans: Electrophiles: The species which have one atom the octet of which is incomplete they attract nucleophiles are called Electrophiles e.g. BF₃ ,Cl⁺ etc

Nucleophiles: The species which carry negative charge or a loan pair of electrons on an atom for donation are called Nucleophiles e.g. HS⁻ , (CH₃)₃N: etc

 LEVEL – 2

1. Write the IUPAC name of the following compound

Ans: The IUPAC name is 2,2,6-trimethylhept-3-ene. 

4. How Sodium fusion extract is prepared ?

Ans: A small piece of dry Sodium metal is heated with an organic compound in a fusion tube for 2-3 minutes and the red hot tube is plunged in to distilled water contained in achina dish The contained of the china dish is boiled ,cooled and filtered . The filtrate is known as Sodium fusion extract.

5. Explain the principle of Paper Chromatography.

Ans: Paper Chromatography is based on the difference in the rates at which the components of a mixture are adsorbed. The material on which different components are adsorbed is called Stationary phase which is generally made up of Alumina, Silica gel or Activated Charcoal.The mixture to be separated is dissolved in asuitable medium and it is called Moving phase. The moving phase is run on the stationary phase, the different compounds are adsorbed on stationary phase at different rates.

LEVEL – 3

1. Write a short note on RESONANCE EFFECT.

Ans: The polarity produced in the molecule by the interaction of two pi bonds or between a pi bond and loan pair of electron present on an adjacent atom is known as RESONANCE EFFECT There are two types of resonance effect:

(1) Positive resonance effect (Transfer of electron is away from an atom or substituent group attached to the conjugated system ) +R effect

e.g. –OH , -OR , -NH₂

(2) Negative resonance (Transfer of electron is towards the atom or substituent group attached to the conjugated system ) –R effect

e.g. –COOH , -CHO , -CN

2. Differentiate between the principles of estimation of nitrogen in an organic compound by

(i) DUMAS method

(ii) KJELDAHL'S method

Ans: (i) Dumas method : A known mass of organic compound is heated with excess of CuO in an atmosphere of CO₂, when nitrogen of the organic compound is converted into N₂ gas The volume of N₂ gas thus obtained is converted into STP and the percentage of nitrogen is determined by the formula.