`text(Occurrence and extraction of mercury)` : Cinnabar (`HgS`) is the only important ore of `Hg`. lt is concentrated by froath floatation method and mercury is extracted from this ore by heating it in air at `773- 873` `K` (auto reduction).

`HgS + O_2 overset(773- 873K)-> Hg + SO_2`

The mercury vapours thus obtained are condense to give liquid metal. `Hg` thus obtained contains impurities of `Zn`, `Sn` and `Pb`. These are removed by treating the impure metal with dil. `HNO_3`. Mercurous nitrate, `Hg_2(NO_3)_2` thus formed reacts with metals present as impurities forming their nitrates which pass into solution leaving behind pure mercury. However, it is best purified by distillation under reduced pressure.

`6Hg + 8HNO_3 (dil.) oversettext(warm)-> 3Hg_2 (NO_3)_2 + 4H_2O + 2NO`

`Zn + Hg_2(NO_3)_2 -> Zn(NO_3)_2 + 2Hg`

Similar reaction is given by `Pb` and `Sn`.

`text(Properties of mercury)` : Mercury is less reactive than `Zn`. It is liquid at room temperature and has low thennal and electrical connectivity. Mercury forms dimeric mercury (I) ion, `Hg_2^(+2)` in which the two `Hg` atoms are bonded by a covalent bond. lt is lowly oxidised to `HgO` at about its boiling point. `Hg` does not react with dil. `HCl` or dil. `H_2SO_4` but reacts with hot concentrated `H_2SO_4` to form `HgSO_4`. It, however, reacts with both warm dil. and conc. `HNO_3` evolving `NO` and `NO_2`, respectively.

`Hg + 2H_2SO_4 text((hot, conc.)) -> HgSO_4 + SO_2 + 2H_2O`

`Hg + 4HNO_3 text((conc.)) -> Hg(NO_3)_2 + 2NO_2 + 2H_2O`