Why is −NH₂ group of aniline acetylated before carrying out nitration?

In Amines, the nitrogen atom bonds with alkyl or aryl groups replacing hydrogen, whereas in amides, the nitrogen atom bonds directly with the carbonyl group (-CO-).

Kjeldahl's method is not applicable to compounds containing nitrogen in nitro and azo groups and nitrogen present in the ring.

$C{H}_{3}C{H}_{2}N{O}_2\stackrel{573K}{\to }C{H}_2=C{H}_2+HN{O}_2$

Correct order of basic strength in aqueous medium is

${\left(C{H}_3\right)}_{2}NH>C{H}_{3}N{H}_2>{\left(C{H}_3\right)}_{3}N>N{H}_3$

Kindly consider the following figure