Redox Reactions And Electrochemistry Ques 652
Question: Zn gives $ H_2 $ gas with $ B_2SO_4 $ and $ HCl $ but not with $ HNO_3 $ because
Options:
A) Zn acts as an oxidising agent when it reacts with $ HNO_3 $
B) $ HNO_3 $ is weaker acid than $ H_2SO_4 $ and $ HCl $
C) In electrochemical series, Zn is above hydrogen
D) $ NO_3^{-} $ is reduced in preference to hydronium ion
Show Answer
Answer:
Correct Answer: D
Solution:
[d] Zinc gives $ H_2 $ , gas with dil $ H_2SO_4/HCl $ but not with $ HNO_3 $ because in $ HNO_3,NO_3^{-} $ ion is reduced and give $ NH_4NO_3,N_2O,NO $ and $ NO_2 $ (based upon the concentration of $ HNO_3 $ )
$ [Zn+\underset{left( nearly6)}{\mathop{2HNO_3}},\xrightarrow{{}}Zn{{( NO_3 )}_2}+2H]\times 4 $
$ HNO_3+8H\xrightarrow{{}}NH_3+3H_2O $ $ NH_3+HNO_3\xrightarrow{{}}NH_4NO_3 $
$ 4Zn+10HNO_3\xrightarrow{{}} $ $ 4Zn{{( NO_3 )}_2}+NH_4NO_3+3H_2O $ Zn is on the top position of hydrogen in electrochemical series.
So Zn displaces $ H_2 $ from dilute $ H_2SO_4 $ and $ HCl $ with liberation of $ H_2 $ . $ Zn+H_2SO_4\to ZnSO_4+H_2 $
