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

Uses

  • 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.
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