Zinc
Zinc is a transition metal with symbol Zn and atomic number 30. It is a useful reducing agent which is readily available. It exists in the oxidation state +2 in solution and may be readily plated out of solution, despite its reducing tendencies. Its compounds are colorless due to the zinc ion's [Ar] 3d10 electron configuration, with a filled d-shell.
Contents
Properties
Physical properties
Zinc is a silvery metal with a bluish cast. Older pieces of zinc may appear to have a white coating of zinc oxide or zinc carbonate on the surface. It has a relatively low melting point of 420 °C.
Chemical properties
Zinc metal is stable in both air and water, but it will react readily with dilute acids. However, extremely pure zinc metal exhibits reduced reactivity towards acids. Zinc is amphoteric and will dissolve in strong bases to form zincates. Zinc dust burns in air with a greenish-white flame to form zinc oxide.
The potential for the reaction Zn2+ + 2e- → Zn is -0.76 V. Despite this, zinc metal can be plated out of solution without issues such as hydroxide formation.
Availability
United States pennies minted after 1982 are relatively pure zinc clad with copper. Because zinc melts at only 420 °C (787.2 °F), it can be melted and cast into the desired shape using a blowtorch or furnace. Though some copper impurities will likely remain, the large difference in the reactivity of the two metals means that most uses of zinc will be unaffected by this.
Zinc metal can be found at boating shops as sacrificial anodes for rust protection. These pieces may contain small amounts of cadmium in them, so they should be handled with care.
Zinc is used as a casing in most zinc-carbon batteries.
Zinc, chemically, can most commonly be purchased as zinc sulfate.
Isolation
Zinc metal can be made by reducing zinc oxide with carbon in a furnace.
Zinc can be prepared via electrowinning from a diluted zinc sulfate solution.
Projects
- Zinc plating
- Building batteries
- Making zinc alloys
- Reducing Cr(III) to Cr(II)
- Making zinc sulfide
- The synthesis of anhydrous aluminium chloride through thermite
Handling
Safety
Zinc is not very toxic by itself. Zinc sacrificial anodes, however, may contain the dangerous metal cadmium, which is notoriously difficult to remove. Zinc dust is flammable, and class-D fire extinguishers should be used to deal with these types of fires. Water may aggravate a zinc fire and should not be used.
Never consume zinc or its compounds, when produced in the laboratory, as a supplement.
Older grades of zinc, and those used in zinc-carbon batteries, may contain arsenic and lead. Upon melting, these emit arsenic compounds into the air as fumes, and are extremely hazardous. Take caution when melting an unknown-purity sample of zinc. Even the purest grades of zinc contain small but significant amounts of cadmium.
Storage
Bulk zinc metal can be stored in any type of container. It slowly develops an oxide layer which further protects from corrosion. Zinc powder should be stored in small bottles, away from open air.
Disposal
Zinc and its compounds have little toxicity and no special disposal is required. Technical grade zinc however, may contain traces of heavy metals, and the zinc waste should be taken to disposal facilities.
References
