Question

What happens in Group II Qualitative Analysis if no precipitate forms after the first step (the addition of HCl and thioacetamide). What can you conclude if no precipitate forms after you add NaOH to the black solid formed from the addition of HCl and thiacetamide?

Answer 1

thiacetamide generate H2S in the solution . and HCl is already present . HCl +H2S mixture now can act as second groups reagent . if no precipitate forms means absence of second group cations.

now on addition of NaOH , just assume . some NaOH utlised for neutralisation of HCl and some NaOH still we have

now H2S is present in basic medium . H2S in basic medium is perfectly for fouth group cations (Ni+2 ,Co+2 , Mn+2 ,Zn+2 ) reagent.

black precipitate formed means there is presence of forth group cation it may be Ni+2 or Co+2