Arsenic

Arsenic, As, is a metallic main group element, found in Group Vb of the periodic table.

Atomic Number : 33
Relative Atomic Mass : 74.92

Arsenic and its compounds are highly toxic.

Discovery

Arsenic was first isolated as the metal by Albertus Magnus about 1250AD.

Occurrence

Arsenic is found in the minerals as oxides, sulphides and arsenides :

Arsenolite, As4O6,
Realgar, As4S2,
Orpiment, As2S2,
Mispickel or Arsenical Pyrite, FeAsS,
Colaltite or Cobalt Glance, CoAsS,
A Tin White Cobalt, CoAs2,
Arsenical Iron, AsFe and As4Fe3,
Nickel Glance, NiAsS, and
Kupfernickel, NiAs.

Extraction

Preparation

Arsenic is prepared in the laboratory by reducing Arsenious Oxide, As4O6, with Carbon.
As4O6 + 3 C ==> As4 + 3 CO2

Manufacture

Arsenic is manufactured by distilling Arsenical Pyrites, FeAsS
FeAsS ==> FeS + As

Properties

Arsenic in its elemental form exhibits allotropy and three forms are known.

gamma-Arsenic which is also known as gray-Arsenic, As, is the ordinary form and it is a steel-gray metallic substance with a bright luster,
beta-Arsenic is formed when the gamma-Arsenic is heated in a stream of Hydrogen and black crystals of beta-Arsenic are deposited nearest the hot end of the tube, and
alpha-Arsenic is formed when the gamma-Arsenic is heated in a stream of Hydrogen and a yellow powder of alpha-Arsenic is deposited in the cooler part of the tube. alpha-Arsenic is very sensitive to light and reverts to gamma-Arsenic.

Reactions

Arsenic is similar in to Calcium in its chemical properties.

Uses

Arsenic has a wide variety of uses in several industries. It is used

in the manufacture of arsenic compounds,
in preparing hardened lead shot (i.e. an alloy of lead and arsenic),
in alloys used for making boiler tubes,
in insecticides and weed-killers,
in the electronics industry in the manufacture of semiconductors, and
Arsenic in the form of Gallium Arsenide is used in semiconductor lasers.

Detection and Analysis

Arsenic is detected by the green colouration of Copper Arsenide, CuAs, which is formed on the surface of Copper foil, Cu, when the arsenic compound is heated with Hydrochloric Acid.

Start of Hypertext .... Elements .... Compounds .... Index