d Block Elements : Murcury and its Compounds

Murcury and its Compounds

Ores : Cinnabar (HgS)

Extraction : Roasting : The concentrated ore roasted at 770 K to 780 K in the pressure of air.

          2HgS + 3SO2 → 2HgO + 2SO2; 2HgO → 2Hg + O2

Refining : By filtering impure  through thick canvass or chamois leather. It is then dropped into 5% HNO3.

Compounds of Mercury

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Mercuric chloride HgCl2 (Corrosive sublimate) : It is a colourless solid, sparingly soluble in water. It forms red ppt. of  with KI HgCl2 + 2KI → HgI2 +2KCl. With NH4OH it gives white ppt. of Hg(NH2)Cl.

HgCl2 + 2NH4OH → Hg(NH2)Cl + NH4Cl + 2H2O.

                                      White ppt.

Mercurous chloride Hg2Cl2 (Calomel) : It is a white solid insoluble in water.  With NH4OH it forms a black mixture composed of black metallic mercury and white mercuric amino chloride, Hg(NH2)Cl

H{ g }_{ 2 }Cl_{ 2 }+2N{ H }_{ 4 }OH\rightarrow \underbrace { Hg+Hg(NH_{ 2 })Cl } +NH_{ 4 }Cl+2H_{ 2 }O

Black Mixture

 It is used as purgative in medicine and it sublimes on heating.

Mercuric iodide :  It is a yellow solid below 400K but changes to red solid above 400K.

HgI2  \xrightleftharpoons[\text{}]{\text{400 K}}  HgI2                            

It dissolves in excess of KI forming K2HgI4; HgI2 + 2KI → K2HgI4

Alkaline solution of K2HgI4 is called Nessler’s reagent.