3. Iodide

1. $Ag^+$ (Silver nitrate)

$I^-$ $+$ $Ag^+$ $\longrightarrow$ $AgI$ - Light yellow, cheesy precipitate - Insoluble in $HNO3$ - Insoluble in $NH_3$ and $S_2O_3^{2-}$ One essential mode of complex formation: $AgI+2CN^-\rightarrow [Ag(CN)_2]^-+I^-$ (->dicyanoargentate)

2. $Cl_2$ (+$CH_3Cl$)

$2I^-+Cl_2$ $\rightarrow $ $2Cl^-+I_2$ (-> purple iodine)

3. $H_2SO_4$ conc

With dry iodide, release of $HI$, which partially dissociates under heat (-> purple iodine)

3. $Pb^{2+}$

- Yellow precipitate (see →     cation $Pb^{2+}$)

3. $Hg^{2+}$

- Red precipitate (see →     cation $Hg^{2+}$)

3. $NO_2^-$ (nitrite)

- Formation of $I_2$ (see anion →     anion $NO_2^-$ )