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Model Paper 10 — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistryModel Paper 105 Marks
Question
1. Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?
2. How does
i. an electron withdrawing group (EWG) and
ii. an electron donating group (EDG) influence the acid strength of carboxylic end?
✓

Answer

1. Nitric acid is added to sodium extract so as to decompose
$
NaCN+HNO_3 \longrightarrow NaNO_3+HCNNa_2 S+2 HNO_3 \longrightarrow 2 NaNO_3+H_2 S
$
2. The influence of the inductive effect on acidity is best understood in terms of the conjugate base, $RCOO ^{-}$and can be summarised as follows
Image
Electron withdrawing group destabilises $RCOO ^{-}$because there exists a repulsion between electrons from EDG and negative charge of O. Hence, EDG weakens the acid.
Image
Electron withdrawing group stabilities $RCOO ^{-}$by taking negative charge from O . Hence, EWG strengthens the acid.

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