Describe the functional group of an alcohol. How alcoholic groups are identified?

 

  1. No.8. Describe the functional group of an alcohol. How alcoholic groups are identified?

Answer. The functional group of alcohols is -OH. Their general formula is ROH, where R is any alkyl group.

For example, methyl alcohol (CH3-OH), ethyl alcohol (CH3-CH2-OH) and n-propyl alcohol (CH3-CH2– CH2-OH)

Identification of alcohol

Alcohol can be identified by sodium metal test. Take about 2-3 cm3 of the given organic liquid in a dry test tube and add a piece of sodium metal. Hydrogen gas will evolve which confirms the presence of alcohol.

Ester formation test:

Heat about 1.0 cm3 of the organic compound with 1.0 cm3 of acetic acid and 1-2 drops of concentrated sulphuric acid. Fruity smell will be given out which confirm the presence of alcohol.

  1. No.9. Differentiate between aldehyde and ketone functional groups. How both are identified from each other?

            O

          ―║―C―H

Answer. Aldehyde consists of as functional group. Theirs general formula is RCHO. For example,                         

                                                O                                            O     

                                               ║                                              ║

H-C-H                                      H-C-C-H

Form aldehyde                                  Acetaldehyde

C=O

Ketone consists of as functional group having general formula

For example,

                    

                    

150px-Formaldehyde-2D.svg

          Acetaldehyde

Aldehyde is identified by Fehling’s solution test. Mix equal volumes of Fehling’s solution A and B in a test tube. Add a pinch of organic compound- and boil for five minutes. Red precipitate will be formed.

While ketone is identified by Phenyl hydrazine test. Shake a of the given organic compound with about 2.0 cm3 of phenyl  hydrazine solution. Orange red precipitate will be formed.

 

Q.No.10. Encircle the functional groups in the following (compounds. Also give the names of the functional groups?

Answer.

(i)     O                           (ii)     O

║                                     ║

CH3-C-CH3                       CH3-C-H

 

(iii)         O                                   (iv)        O

║                                      ║

HO-C-CH2-CH3                H-C-CH2-CH3

 

(vi)             O

(v)       H2C = CH – CH3        CH3-O-C-CH3

 

(i) Ketone      (ii) Aldehyde          (iii) Carboxylic acid (iv)  Aldehyde

(v) Alkane    (vi) Ester

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