CBSE Class 10 Science 2020 Outside Delhi Set 2

Question : 5 of 7

Marks: +1, -0

(a) Carry out following conversions :
(i) Ethanol to Ethene
(ii) Ethanol to Ethanoic acid
(b) Differentiate between addition reaction and substitution reaction. Give one example of each.

Solution:

(a) (i) Conversion of ethanol to ethene: Heating ethanol at

443 {\K}

with excess concentrated sulphuric acid results in the dehydration of ethanol to give ethene.

{ {\CH}_3- {\CH_2 \OH}}↙{\text "Ethanol"}{─────▶}↙{\H_2\SO_4}↖{\;\text " Hot conc. "\;} {\CH_2= \CH_2}↙{\text "Ethene"}+ \H_2 \O

The concentrated sulphuric acid can be regarded as a dehydrating agent which removes water from ethanol.
(ii) Conversion of ethanol to ethanoic acid:
Ethanol can be converted to ethanoic acid in the presence of alkaline

{\KMnO}_4

and by heating the solution to give the ethanoic acid.

{{\CH_3-\CH_2\OH} }↙{\Ethanol}\;{──────────────▶}↖{\;\text " Alkaline "\KMnO_4 +\Heat }↙{\text "Or acidified "\;\K_2 \Cr_2\O_7+\;\text " Heat "\;}{\CH_3\COOH}↙{\text "Ethanoic acid"}

(b) Difference between addition and substitution reaction :

S.No	Addition reaction	Substitution reaction
1	It is the combination of two or more atoms or molecules in order to form a large molecule.	The large molecules formed after the reaction is called the adduct.
2	The large molecules formed after the reaction is called the adduct.	The leaving group or the molecular components which leave the reaction and are being replaced are called substrates.
3	No by-product is formed.	A by-product is formed.

Example of addition reaction :
Addition reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains.

Example of substitution reaction:
In the presence of sunlight, chlorine is added to hydrocarbons in a very fast reaction. Chlorine can replace the hydrogen atoms one by one. Thus these reactions are used in the synthesis of the intermediates.

{\CH}_4+ {\Cl}_2 {───────────▶}↖{\;\text " (in the presence of sunlight) "\;} {\CH}_3 {\Cl}+ {\HCl}

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