2019 has been declared by UNESCO as the Year of the Periodic Table. To celebrate, we are releasing a series of blogs about our favourite elements and their importance to the chemical industry. Today we look at mercury and some of its reactions.
Mercury is a silver, heavy, liquid metal. Though mercury is a liquid at room temperature, as a solid it is very soft. Mercury has a variety of uses, mainly in thermometers or as an alloy for tooth fillings.
Mercury & Aluminium
Mercury is added directly to aluminium after the oxide layer is removed. Source: NileRed
The reaction between mercury and aluminium forms an amalgam (alloy of mercury). The aluminium’s oxide layer is disturbed When the amalgam forms, in the following reaction:
Al+ Hg → Al.Hg
Some of the Al.Mg get’s dissolved in the mercury. The aluminium from the amalgam then reacts with the air to form white aluminium oxide fibres, which grow out of the solid metal.
Mercury & Bromine
Mercury and bromine are the only two elements that are liquid at room temperature on the periodic table. Source: Gooferking Science
When mercury and bromine are added together they form mercury(I) bromide in the following reaction:
Hg2 + Br2 → Hg2Br2
This reaction is unique as mercury can form a metal-metal covalent bond, giving mercury(I) bromide a structure of Br-Hg-Hg-Br
Making the Pharaoh's Serpent by igniting mercury (II) thiocyanate. Source: NileRed
The first step of this reaction is to generate water-soluble mercury (II) nitrate by combining mercury and concentrate nitric acid. The reaction goes as follows:
Hg + 4NO3 → Hg(NO3)2 + 2H2O + 2NO2
Next, the reaction is boiled to remove excess NO2 and convert mercury(I) nitrate by-product to mercury (II) nitrate. The mixture is them washed with water and potassium thiocyanate added to the mercury (II) nitrate:
Hg(NO3)2 + 2KSCN→ Hg(SCN)2 + 2KNO3
The mercury (II) thiocyanate appears as a white solid. After this is dried, it can be ignited to produce the Pharaoh’s serpent, as it is converted to mercury sulfide in the following reaction:
Hg(SCN)2 → 2HgS + CS2 + + C3N4
The result is the formation of a snake-like structure. Many of the final products of this process are highly toxic, so although this used to be used as a form of firework, it is no longer commercially available.
Though many reactions of mercury look like a lot of fun, mercury and many of it’s products is highly toxic - so don’t try these at home!