CBSE Class 12 Chemistry 2016 Delhi Set 1 Solved Paper

Question : 25 of 26

Marks: +1, -0

Write the structures of A, B, C, D and E in the following reactions:

OR
(a) Write the chemical equation for the reaction involved in Cannizzaro reaction.
(b) Draw the structure of the semicarbazone of ethanal.
(c) Why

{\pK}_a

{\F}- {\CH}_2- {\COOH}

is lower than that of

{\Cl}- {\CH}_2- {\COOH}

?
(d) Write the product in the following reaction
(e) How can you distinguish between propanal and propanone?

Solution:

OR
(a)

2 {\HCHO}  \ {─────▸}↖{50 \% \ {\NaOH}} {\CH}_3 {\OH}+ {\HCOONa}

(b)

{\CH}_3- {\CH}= {\N}- {\NH}- {\CO}- {\NH}_2

{\FCH}_2- {\COOH}

, fluorine is more electron withdrawing than chlorine in

{\ClCH}_2- {\COOH}

, so

{\FCH}_2- {\COOH}

, flurine is more acidic than

{\ClCH}_2 {\COOH}

hence its

{\pK}_a

value is lesser than

{\ClCH}_2 {\COOH}

.
(c)

{{\CH}_3- {\CH}= {\CH}- {\CH}_2- {\CN}}↙{\Pent-3-\enenitrile} \;{{   {─────▸}↖{\;\text " (i) "\; {\DIBL-{\H}}}↙{{\;\text " (i) "\; {\H}_2 {\O}}} }}

{ {\CH}_3- {\CH}= {\CH}- {\CH}_2- {\CHO}}↙{\Pent-3-\ene-1-\al}

(e) Propanal and propanone can be differentiated by Tollens' reagent i.e., propanal will give silver mirror but propanone will not.

{\CH}_3- {\CH}_2- {\CHO}+2 [ {\Ag} ( {\NH}_3) _2] ^{+} → {\CH}_3- {\CH}_2

- {\COO}^{-}+2 {\Ag}

+ {{\H}_2 {\O}+4 {\NH}_3 }↙{\Silver \mirror}

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