Question of salt analysis : For nitrate test : sample salt + conc H2SO4 ; adding Cu pellets will - Chemistry - Equilibrium

Question

Question of salt analysis :
For nitrate test : sample salt + conc H2SO4 ; adding Cu pellets
will result in formation of brown gas which shows presence of
nitrate ion
Reactions : NO3 - + H2SO4 == HSO4
- + HNO3
4 HNO3 + Cu == Cu(NO3) + 2 NO2 (brown gas) + 2 H2O

Why this reaction won't follow if dilute H2SO4 were used instead of
conc H2SO4 ?

Geetha · Accepted Answer

Concentrated sulphuric acid reacts with the nitrate ion to form
nitric acid Nitric acid then reacts with the copper turning forms
nitrogen monoxide Nitrogen monoxide is further oxidized to nitrogen
dioxide Dilute sulphuric acid cannot remove completely nitrate ion
from the salt Only partial removal occur The complete formation of
nitric acid is needed as it acts as an oxidising agent too