Zinc: an orchestral metal

Zinc properties and areas of application

In­tro­duc­tion

Zinc is a bluish-white met­al coat­ed with an ox­ide film. Its melt­ing point is 420°C (787°F). Zinc pow­der tints flames a beau­ti­ful sky-blue col­or. Zinc is the 24th most com­mon chem­i­cal el­e­ment on Earth. The most wide­ly-used zinc ore is spha­lerite – zinc sul­fide with iron im­pu­ri­ties.

Dis­cov­ery his­to­ry

Zinc and cop­per form an al­loy called brass, which was known thou­sands of years be­fore the dis­cov­ery of zinc as a sep­a­rate el­e­ment. Zinc as a sep­a­rate el­e­ment was sup­pos­ed­ly dis­cov­ered in In­dia around 1300. How­ev­er, the dis­cov­ery of pure zinc is of­ten at­trib­uted to Ger­man chemist An­dreas Marggraf, as he de­scribed the process in de­tail.

Chem­i­cal prop­er­ties

Zinc is an ac­tive met­al and can be used as a re­duc­ing agent to pro­duce oth­er, less ac­tive met­als. For ex­am­ple, it can re­cov­er tin from an acid­i­fied aque­ous so­lu­tion of tin(II) chlo­ride.

SnCl₂ + Zn → Sn + Zn­Cl₂

Zn + Sn²⁺→ Sn + Zn²⁺

When heat­ed, zinc re­acts with sul­fur, pro­duc­ing smoke con­sist­ing of zinc sul­fide and sul­fur. The mix­ture burns with a bright yel­low-green flame.

Zn + S → ZnS

Zinc has am­pho­ter­ic prop­er­ties, mean­ing that it can in­ter­act with both acids and al­ka­lis. It dis­solves vig­or­ous­ly in acids, such as hy­drochlo­ric acid, and re­acts slow­ly in al­ka­line so­lu­tions.

Zn + 2HCl = Zn­Cl₂ + H₂

Zn + 2NaOH + 2H₂O = Na₂[Zn(OH₄)] + H₂

Zinc in­ter­acts with io­dine with the ad­di­tion of a few drops of wa­ter. The mix­ture heats up and some of the io­dine sub­limes, form­ing a vi­o­let va­por.

Zn + I₂ = ZnI₂

Zinc hy­drox­ide is in­sol­u­ble in wa­ter, but dis­solves in an ex­cess of al­ka­li

Zn(OH)₂ + 2NaOH = Na₂[Zn(OH₄)]

Ap­pli­ca­tion

Zinc is used to make al­ka­line and zinc-car­bon bat­ter­ies. Many mu­si­cal in­stru­ments, such as sax­o­phones, are made of brass. As zinc coat­ings can pro­tect oth­er met­als from cor­ro­sion, iron bolts and screws are of­ten zinc-plat­ed, or gal­va­nized. This “zinc de­fense” even saves ships from cor­ro­sion by sea­wa­ter. Zinc ox­ide is used as a white pig­ment.

Bi­o­log­i­cal role

Zinc is an es­sen­tial trace el­e­ment for hu­mans, es­pe­cial­ly chil­dren. Zinc de­fi­cien­cy can stunt growth, harm the eyes, and hurt the skin. Nu­tri­tion­al sup­ple­ments con­tain­ing zinc com­pounds are used to treat zinc de­fi­cien­cy.

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