why we should add dilute sulphuric acid to mohr’s salt?

Mohr's salt consists the salt of ferrous sulfate and ammonium sulfate, both of which are salts of a solid corrosive and powerless bases. In this way, in watery arrangement, the cations of both experience hydrolysis according to the accompanying equilibria: 

Fe(2+) + H2O = FeOH(+) + H+ 

NH4+ + H2O = NH4OH + H+ 

At the point when the centralization of the H+ particle is expanded by including somewhat corrosive, the harmony will be moved to one side, stifling the hydrolysis. Therefore, sulphuric corrosive is added to keep the hydrolysis of the salt so that the nature of the essential standard is kept up to get precise outcomes.