In the diazotisation of arylamines with sodium nitrite and hydrochloric acid, an excess of hydrochloric acid…
In the diazotisation of arylamines with sodium nitrite and hydrochloric acid, an excess of hydrochloric acid is used primarily to
supress the concentration of free aniline available for coupling
supress hydrolysis of phenol
ensure a stoichiometric amount of nitrous acid
neutralise the base liberated
Solution
Excess of $\mathrm{HCl}$ is used to convert free aniline to aniline hydrochloride otherwise free aniline would undergo coupling reaction with benzenediazonium chloride.
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