Organic Chemistry Important Question

Q1. Process of separation of mixtures into their components and to purify the compounds by using adsorption is known as:

  • 1) Distillation
  • 2) Sublimation
  • 3) Chromatography
  • 4) Differential extraction

Solution

Process of separation of mixtures into their components and to purify the compounds is known as chromatography.

Q2. Rate of reaction of alkanes with halogens is:

  • 1) F2>Cl2> Br2> I2
  • 2) Br2> I2>F2>Cl2
  • 3) Cl2> Br2>F2> I2
  • 4) Cl2> Br2> I2>F2

Solution

Rate of reaction of alkanes with halogens is F2>Cl2> Br2> I2.

Q3. Alkyl radical stability increases as we proceed from:

  • 1) Ethyl free radical<Methyl free radical< Isopropyl free radical
  • 2) Methyl free radical<Ethyl free radical< Isopropyl free radical
  • 3) Ethyl free radical< Isopropyl free radical<Methyl free radical
  • 4) Isopropyl free radical< Methyl free radical<Ethyl free radical

Solution

Alkyl radical stability increases as we proceed from Methyl free radical<Ethyl free radical< Isopropyl free radical as more hyperconjugating structures are formed as we proceed from methyl to Isopropyl.

Q4. Write the position isomers of C3H8O.

Solution

C3H8O represents following position isomers

4ch

Q5. What is a homolytic cleavage?

Solution

In hemolytic cleavage one of the electrons of the shared pair in a covalent bond goes with each of the bonded atoms. Thus in this movement of a single electron takes place instead of an electron pair.

Q6. Which of the following ions is most stable?

  • 1) CH3CH2 – CH2+
  • 2) (CH3)3C+
  • 3) 63ch 1
  • 4) (CH3)3C – CH2+

Solution

Tertiary carbonium ions are most stable due to hyperconjugation effect and +I effect of methyl group.

Q7. What is the order of rate of reaction of alkanes with halogens F2, Cl2, Brand I2?

Solution

The order of rate of reaction of alkanes with halogens is F2 > Cl2 > Br2 > I2.

Q8. What are the different types of structural isomers?

Solution

Different types of structural isomers are chain isomerism, position isomerism, functional group isomerism and metamerism.  

Q9. In sulphur estimation, 0.157 g of an organic compound gave 0.4813 g of barium sulphate. The percentage of sulphur in the compound is:

  • 1) 42.10%
  • 2) 43%
  • 3) 34%
  • 4) 34.04%

Solution

Molecular mass of BaSO4 = 137+32+64 = 233 g 233 g BaSO4 contains 32 g sulphur 0.4813 g BaSO4 contains = 32 X 0.4813/ 233 g sulphur Percentage of sulphur=32X 0.4813 X100/ 233 X 0.157 = 42.10%

Q10. When nitrogen and sulphur are both present in an organic compound, what is the test to perform?

Solution

When nitrogen and sulfur are both presents in an organic compound, sodium thiocyanate is formed and it gives blood red color.  Na + C + N+ S  15004 arrow NaSCN  Fe3+  +  SCN 15004 arrow  [ Fe (SCN) ]2+     Blood red

Q11. What is fractional distillation process?

Solution

When the difference in boiling points of two liquids is not much, simple distillation cannot be used to separate them. The vapours of such liquids are formed within the same temperature range and are condensed simultaneously. The technique of fractional distillation is used in such a process.

Q12. The correct representation of 4-hydroxy-2-methylpent-2-en-1-al is:

Solution

The correct representation of 4-hydroxy-2-methylpent-2-en-1-al is:

12ch

Q13. What is the electrophilic centre in the molecule CH3CN?

Solution

In the molecule CH3CN, the starred carbon atom is the electrophilic centre as has partial positive charge due to polarity of bond. 

13ch

Q14. How can you separate aniline from aniline-water mixture?

Solution

Steam distillation technique is applied to separate substances which are steam volatile and are immiscible with water like aniline from aniline-water mixture.

Q15. What is the violet color due to, when sodium fusion extract is treated with sodium nitroprusside in the test for sulfur?

Solution

On treating sodium fusion extract with sodium nitroprusside, the appearance of a violet color due to the formation of [Fe(CN)5NOS]4- indicates the presence of sulfur.

Q16. What is chain isomerism? Give example.

Solution

Two or more compounds which have a similar molecular formula but different arrangement of carbon atoms in straight or branched chains are referred to as chain isomers, and the phenomenon is known as chain isomerism. For example C5H12 represents three compounds. 

16ch

Q17. Discuss the order of stability of the carbocation 

17ch

Solution

Carbocations are highly unstable and reactive species. Alkyl groups directly attached to the positively charged carbon stabilize the carbocation due to inductive and hyperconjugation effects. So the order of stability of the carbocation is: 

17ach

Q18. 

18qch

Solution

18ach

2,3-dimethylpentanoyl chloride.

Q19. What is adsorption chromatography?

Solution

Adsorption chromatography is based on the fact that different compounds are adsorbed on an adsorbent to different degrees. Commonly used adsorbents are silica gel and alumina.

When a mobile phase is allowed to move over a stationary phase the components of a mixture move by varying distances over the stationary phase.

Q20. What is Rf value?

Solution

Distance moved by the substance from the base line to the distance moved by the solvent from the base line is known as the Rf value.  

Q21. What is lead-sulphide test for sulphur?

Solution

The sodium fusion extract is acidified with acetic acid and lead acetate is added to it. A black precipitate of lead sulphide indicates the presence of sulphur.   S2-   +  Pb2+   →    PbS Black

Q22. Categorize the following ions as nucleophile or electrophile? HS, BF3, NO2+, C2H5O, NH2

Solution

Nucleophile among the following are : HS, C2H5O, NH2 Electrophile among the following are : BF3, NO2+

Q23. What is the Prussian blue color due to in the test for nitrogen?

Solution

In the test of nitrogen the Prussian blue color formed is of ferriferrocyanide.

Q24. How to detect percentage of oxygen in an organic compound?

Solution

The percentage of oxygen in an organic compound is detected by the difference between the total percentage and the sum of percentages of all other elements present.

Q25. Discuss the shape of CH3+ ion?

Solution

The shape of methyl carbonium ion is derived from the overlap of three equivalent C(sp2) hybridized orbitals with 1s orbital of each of the three hydrogen atoms. Each bond may be represented as C(sp2)H(1s) sigma bond. The remaining carbon orbital is perpendicular to the molecular plane and contains no electrons13fdbfce aa1a 4980 a025 6ef7feae1e2d

25ch

Shape of methyl cation

Q26. Which technique one can employ to separate crude oil in petroleum industry?

Solution

Fractional distillation technique can be used to separate crude oil in petroleum industry.

Q27. What are the three steps in the halogenation reaction?

Solution

Three steps in halogenation reaction are initiation, propagation and termination.

Q28. What are optically active and optically inactive compounds? 

Solution

When plane-polarized light is passed through a substance, it may or may not rotate the plane of the plane-polarized light.

The substance which does not rotate the plane of the plane-polarized light is known as an optically inactive compound, while a substance that rotates the plane of the plane-polarized light is known as an optically active substance.

Q29. How will you test for phosphorus in an organic compound?

Solution

The organic compound is heated with an oxidizing agent. The phosphorus present in the compound is oxidized to phosphate. The solution is boiled with nitric acid and then treated with ammonium molybdate. A yellow coloration indicated the presence of phosphorus. 

29ch

Q30. What is Lassaigne’s test?

Solution

Nitrogen, sulphur, halogens and phosphorus present in an organic compound are detected by Lassaignes test. The elements present in the compound are converted from covalent form to ionic form by fusing the compound with sodium metal. 

30ch

Q31. What is Metamerism?

Solution

Metamerism arises due to different alkyl chains on either side of the functional group in the molecule.

Q32. What are the common techniques used for purification of organic compounds?

Solution

The common techniques used for purification are: Sublimation, Crystallisation, Distillation, Differential extraction and Chromatography.

Q33. How can be covalent bonds cleaved?

Solution

Covalent bonds can be cleaved by homolytic and heterolytic cleavage.

Q34. What is crystallization process?

Solution

This is a technique for the purification of solid organic compounds. It is based on the difference in the solubilities of the compound and the impurities in a suitable solvent. The impure compound is dissolved in a solvent in which it is sparingly soluble at room temperature.

The solution is concentrated to get a nearly saturated solution. On cooling, the solution pure compound crystallizes out and is removed by filtration.

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