Sunday, October 21, 2012

Carbon and its Compounds class 10 CBSE | NCERT Solutions

NCERT Solution, MCQs, Study Notes, Q & A

1.Define the term, functional group and give two examples for it. 

Ans:
An atom or a group of atoms on which properties of the carbon compound depends is known as functional group. Eg: -
OH-            Alcoholic
- CHO        Aldehydic
- CO           Ketonic
 - COOH     Carboxylic

2. Name the functional groups present in the following compounds.

CH3CH2CH2-OH;  CH3CH2CH2COOH ; CH3-CH2-CHO;CH3COCH2CH2CH3
 Ans:
CH3CH2CH2-OH          Alcoholic
 CH3CH2CH2COOH     Carboxylic
CH3-CH2-CHO              Aldehydic
CH3COCH2CH2CH3      Ketonic

3. Describe the preparation of ethanol by the fermentation process. 

Ans:Fermentation of sugar is a process in which the sugar molecules are broken down in the ethylalcohol and carbon dioxide by the action of enzymes called invertage and zymase which are present in yeast. Molasses the bi-product of the sugar industry is mixed with suitable quantity of water and yeast powder. This mixer is kept in a huge steel tank at 250C to 300C for about 10 to 12 days, during this time fermentation takes place to form C2H5OH and CO2 gas. C2H5OH is recovered from this mixture by distillation.
                                   Invertase
C12 H22 O11 + H2O  -------------->        C6H12O6           +          C6H12O6
                               (From yeast)            Glucose                          fructose
           Zymase
C6 H22 O16                                       ----------------->  2C2H5OH + 2CO2
Glucose & Fructose                   (from yeast)                        Ethanol

4. What is meant by denaturated alcohol ? How is it prepared?

Ans:
Ethyl alcohol (ethanol) made into unfit for drinking is called denaturated alcohol.
It is prepared by adding poisonous substances like menthol, pyridine,  copper sulphate etc., to ethanol.

5. Give the names of the following :
i) an aldebyde derived from ethane
 ii) A ketone derived from butane
iii) The compound obtained by oxidation of ethanol by chromic anhydride (CrO3); and
iv) The substance formed on catalytic hydrogenation of methanal

Ans
(i) Ethanal (Or)Acetaldehyde CH3CHO
( ii) 2-Butanone (Or) Butanone-2 CH3COCH2CH3
(iii) Ethanal (Or)Acetaldehyde CH3CHO
(iv) Methane CH4

5. How is ethanoic acid prepared commercially from methanol ?

Ans:  Ethanoic acid is prepared commercially by reaction between methanol and carbon monoxide in the presence of Iodine - rhodium catalyst.
                                     I2-Rh
CH3OH + CO   ------------------> CH3COOH

6. Explain the follwing terms: (i)Esterification (ii)saponification (iii) decarbodylation

Ans: Esterification:- The reaction of carboxylic acid with an alcohol to form ester in the presence of conc. H2SO4 know as Esterifilation reaction.
CH3COOH + C2H5OH --------------à CH3COOC2H5 + H2O
Saponification : oil or a fat on heating with sodium hydroxide (NaOH) Solution forms sodium salt of carboxylic acid (soap)and glycerol, this reaction is know as saponification reaction.
CH2 – O COR                         CH2OH
|                                                  |
CH – O COR + 3NaOH       CHOH + 3RCOO Na
|                                                  |
CH2 – O COR       --------->        CH2OH

Decarboxylation: Sodium salt of ethanoic acid and soda lime on heating forms methane gas. This reaction is known as Decarboxylation reaction.
CH3COONa + NaOH         ------------->      CH4 + Na2CO3

7. Write chemical equations of the reactions of ethanoic acid with i)sodium (ii) sodium carbonates (iii) ethanol in presence of conc. H2SO4 and (iv) soda lime

Ans: (i) 2 CH3COOH + 2Na ------------------>2CH3COONa + H2­
 (ii) 2CH3COOH + Na2CO3  --------------------------->  2CH3COONa + CO2 + H2O
(iii) CH3COOH + C2H5OH  -------------------------->     CH3COOC2H5 + H2O
(iv) CH3COOH + NaOH   ---------  ----------------------> CH4 + Na2CO3


8. “Saturated hydrocarbons burn with a blue flame while unsaturated hydrocarbons burn with a sooty flame”. Why?

Ans: It is because a saturated hydrocarbon undergoes complete combustion due to high amount of carbon.
C2H6 (CNG) + 7O2 ---------------> 4CO2 + 6H2O + Heat

9. How ethanoic acid got its name as glacial acetic acid?

Ans: Ethanoic acid  has melting point is 290K so it often freezes during winter and looks like glacier. Therefore, it is also known as glacial acetic acid.

10. Name the products obtained on complete combustion of ethanol.

Ans: Carbon dioxide water and Heat

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