Write the balanced chemical equations for the following :
(a) `Pb_(3)O_(4)` is treated with nitric acid.
(b) Zinc oxide is treated with excess of sodium hydroxide solution.
(c) Dilute nitric acid is slowly reacted with metallic tin.
(d) Gold is dissolved in aqua regia.
(e) Iron reacts with cold dilute nitric acid.
(f) Sodium thiosulphate is added slowly to silver nitrate.
(g) Heating of `ZnCI_(2).2H_(2)O`.

Explanation

(a) `Pb_(3)O_(4)` is a mixed oxide, `2PbO.PbO_(2)`. With nitric acid PbO is converted to `Pb(NO_(3))_(2)` while `PbO_(2)` remains as such.
`Pb_(3)O_(4) + 2HNO_(3) rarr PbO_(2) + Pb(NO_(3))_(2) + H_(2)O`
(b) ZnO is dissolved as zincate ion.
`ZnO + 2NaOH rarr Na_(2)ZnO_(2) + H_(2)O`
(c) Tin reduced nitric acid (dilute) to ammonia.
`4Sn + NO_(3)^(-) + 10 H^(+) rarr 4 Sn^(2+) + NH_(4)^(+) + 3H_(2) O`
(d) Gold dissolves in aqua regia as `HAuCI_(4)`.
(e) `4Fe + 10 HNO_(3) rarr 4Fe (NO_(3))_(2) + NH_(4)NO_(3) + 3H_(2)O`
(f) White precipitate changes to yellow, brown and finally becomes black.
`{:(S_(2)O_(3)^(2-) + Ag^(+) rarr underset(("White"))(Ag_(2)S_(2)O_(3))),(Ag_(2)S_(2)O_(3) + H_(2)O rarr underset(("Black"))(Ag_(2)S) + H_(2)SO_(4)):}`
(g) `ZnCI_(2).2H_(2)O overset(Delta)rarr ZnCI(OH) + HCI + H_(2)O`