REACTIONS OF MERCURY

Mercury is a metal and reacts similarly to the other metals in the d-block. Mercury can react to form conventional salts in the +1 or +2 oxidation states but it can also react with organic compounds to form organomercury compounds which are highly toxic.

SOME REACTIONS OF MERCURY

Mercury reacts with oxygen at 350°C to form mercury (II) oxide:

2Hg + O2 → 2HgO (red solid)

Above 400°C HgO decomposes back to its elements and this decomposition was important in the discovery of oxygen as an element by J. Priestley and A. L. Lavoisier.

PRIESTLEY AND LAVOISIER

  

www.thoemmes.com/ gallery/image362.htm        http://iesfelanitx.webcindario.com/cientifics.htm

Mercury reacts with all the halides to give mercury (II) salts sometimes called mercuric halides:

Hg + F2 → HgF2 (white solid)

Hg + Cl2 → HgCl2 (white solid)

Hg + Br2 → HgBr2 (white solid)

Hg + I2 → HgI2 (red solid)

These halides can be converted into mercury (I) halides by combination with metallic mercury. Mercury (I) halides are known as mercurous halides. The example below is shown for mercury chloride:

HgCl2 + Hg → Hg2Cl2 (calomel)

Mercury will only react with oxidising acids such as concentrated nitric acid and hot concentrated sulphuric acid forming mercury (II) salts with oxides of sulphur and nitrogen. Mercury reacts slowly with dilute nitric acid in the following reaction:

2Hg + 2HNO3 → Hg2(NO3)2 + H2

Mercury also alloys with other metals to form so called amalgams. The other metal becomes dissolved in the mercury. Mercury forms amalgams with most heavy metals including gold which is useful in the purification of gold and gold plating. It can also form an amalgam with sodium forming a powerful reducing agent.

Organomercury compounds can be formed by the reaction of sodium amalgam with alkyl halides where R is an organic group and X is a halide:

2Hg + 2RX → HgR2 + HgX2

HgX2 + 2Na → Hg + 2NaX

They can also be formed by reaction of HgCl2 Grignard reagents in tetrahydrofuran:

RMgX + HgCl2 → RHgCl + MgXCl

RMgX + RHgCl → HgR2 + MgXCl

Organomercury compounds (HgR2) are usually highly toxic liquids.