Bismuth: how to grow rainbow crystals
Bismuth properties and areas of application
Bismuth is a lustrous silvery metal with a pink tint and a melting point of 271.5 °С (520.7 °F). One interesting aspect of bismuth is its fascinating crystals, which boast a characteristic stair-stepped structure and can display a wide variety of colors – from yellow to dark blue. Their structure is due to the fact that the crystals grow much more quickly on outer surfaces than on inner surfaces, and their colors are due to an oxide film (Bi₂O₃) that varies in color depending on its thickness. In contrast to its groupmates and period-mates such as antimony, lead, and arsenic, bismuth is one of the few heavy elements which is practically non-toxic. Bismuth and its alloys are thus growing increasingly popular as substitutes for lead. Curiously, within the periodic table, bismuth is considered the last stable element: all subsequent elements are radioactive and have no stable isotopes. It is worth noting, however, that bismuth is only relatively stable. Scientists recently determined the half life of ²⁰⁹Bi to be 1.9 ∙10¹⁹ years – approximately a billion times the age of the universe.
History of discovery
Bismuth was discovered in the 15th century, but it is difficult to say exactly when and by whom. It was thought to be either lead, tin, or antimony until the 18th century, when J. Pott and C. Geoffroy established that bismuth was distinct from other metals and proposed considering it a separate element entirely.
Chemical properties and obtainment
In the laboratory, bismuth can be isolated from an acidified solution of bismuth(III) nitrate (Bi(NO₃)₃) by adding zinc (Zn):
Bi(NO₃)₃ + Zn = Zn(NO₃)₂ + Bi↓
Metallic bismuth dissolves in concentrated nitric acid (HNO₃), forming bismuth(III) nitrate, nitrogen dioxide (NO₂), and water (H₂O):
Bi + 6HNO₃ = Bi(NO₃)₃ + 3NO₂↑ + 3H₂O
Bismuth(III) nitrate hydrolyzes in water, forming shimmering crystals of bismuth(III) oxynitrate (BiОNO₃):
Bi(NO₃)₃ +H₂O = BiОNO₃ + 2HNO₃
Mixing solutions of iodic acid(HIO₃) and bismuth(III) nitrate forms a white precipitate of bismuth(III) iodate (Bi(IO₃)₃):
Bi(NO₃)₃ + 3HIO₃ = Bi(IO₃)₃ + 3HNO₃
- Bismuth is used to make fusible alloys such as Wood’s alloy, which is used as a solder.
- Bismuth vanadate has largely replaced toxic cadmium sulfide as a yellow pigment in paints.
- Bismuth(III) subsalicylate is sometimes used in medicine to treat digestive issues.
- Bismuth(III) oxide creates the sparkle effect in various fireworks.
- Bismuth oxychloride is used as an additive to create a pearly sheen.
- Bibrocathol, a medicine used to treat eye infections and swelling, is based on organic bismuth(III) compounds.
- Bismanol, an alloy of bismuth and manganese, is used to make magnets
- Bismuth germanate is utilized in CAT scanners.