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CBSE Class 10 Science 2023 Delhi Set 1

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Question : 34
Total: 39
(A) (i) Draw the structure of the following compounds:
(a) Butanoic acid
(b) Chloropentane
(ii) How are structure (i) and structure (ii) given below related to one another? Give reason to justify your answer.
Draw one more possible structure for above case.
(iii) Differentiate between saturated and unsaturated carbon compounds on the basis of their general formula.
OR
(B) (i) What happens when a small piece of sodium is dropped in ethanol? Write the equation for this reactions.
(ii) Why is glacial acetic acid called so?
(iii) What happens when ethanol is heated at 443K in the presence of conc. H2SO4 ? Write the role of conc. H2SO4 in this case.
(iv) Write an equation showing saponification.
Solution:  
(A) (i) (a) H−
H
|
C
|
H
−
H
|
C
|
H
−
H
|
C
|
H
−
O
||
C
−OH
(b) H−
H
|
C
|
H
−
H
|
C
|
H
−
H
|
C
|
H
−
Cl
|
C
|
H
−
H
|
C
|
H
−H
(ii) Both are isomers of compound with chemical formula C6H14. Structure (i) is 2,3-dimethylbutane whileStructure (ii) is 2,2-dimethylbutane. One more isomer is, 3-methylpentane.
CH3−CH2−
C
|
‌‌‌‌CH3
H−CH2−CH3
(iii) Saturated carbon compounds always follow the general formula of CnH2n+2. In case of unsaturated carbon compounds, they always follow the general formula CnH2n if there is a carbon-carbon double bond and formula CnH2n−2 if there is a carbon-carbon triple bond.
OR
(B) (i) Alcohols react with sodium leading to the evolution of hydrogen.
2‌Na+2CH3CH2‌OH→
2CH3CH2O−Na+
(Sodium ethoxide)
+H2↑
(ii) The melting point of pure ethanoic acid is 290K and hence it often freezes during winter in cold climates. This gave rise to its name glacial acetic acid.
(iii) Heating ethanol at 443K with excess concentrated sulphuric acid results in the dehydration of ethanol to give ethene. In this case, concentrated sulphuric acid act as a dehydrating agent as at removes water from ethanol.
ethanol.
CH3−CH2‌OH‌
‌ Hot Conc. ‌
───────▶
443KH2SO4
CH2=CH2+H2O
(iv) On treating with sodium hydroxide, which is an alkali, the ester is converted back to alcohol and sodium salt of carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap. Soaps are sodium or potassium salts of long chain carboxylic acid.
CH3COOC2H5
NaOH
───────▶
C2H5‌OH+CH3‌COONa
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