[hal03]

With the fact, I will like to know why at the time of the diazotization of aniline we must add this last(aniline) by small portions to the diluted solution of H2SO4.Et why the experiment must be done with 5°c.
Please help me

[AWK]

Diazonium salts are not thermally stable, some of them decompose even at -30 C.
During reaction of diazotization uou use acid for decomposing of nitrite and for salt formation. Any strong acid can be used, except that with remarkable oxidizing or reducing properties. This may also depend on the purpose, eg using HBF4, during thermal decomposition you can obtain fluorides, eg fluorobenzene from aniline.

[synthetic]

In fact HONO (NO+)  is what reacts. HONO is made of NaNO2 and H+.