Zinc

Chemical reactions




Reaction of zinc with acids


Zinc metal dissolves slowly in dilute sulphuric acid to form Zn(II) ions and hydrogen, H2. In aqueous solution the Zn(II) ion is present as the complex ion [Zn(H2O)6]2+.

Zn(s) + H2SO4(aq) Zn2+(aq) + SO42−(aq) + H2(g)


Zinc is dissolved in concentrated nitric acid, HNO3 [6]:

Zn(s) + 4 HNO3(aq) Zn(NO3)2(aq) + 2 NO2(g) + 2 H2O(l)


Reaction of zinc with air


Zinc reacts with oxygen in moist air. The metal burns in air to form zinc(II) oxide, a material that goes from white to yellow on prolonged heating.

2 Zn(s) + O2(g) 2 ZnO(s) [white]


Reaction of zinc with ammonia


Zn(II) is precipitated by ammonia ions as Zn(OH)2 (white amorphous precipitate)

Zn2+(aq) + 2 NH3(aq) + 2 H2O(l) Zn(OH)2(s) + 2 NH4+(aq)

By excess ammonia, the precipitate is dissolved [1]

Zn(OH)2(s) + 4 NH3(aq) [Zn(NH3)4]2+(aq) + 2 OH(aq)


Reaction of zinc with halogens


Zinc will react with gaseous bromine, Br2, and iodine, I2.

Zn(s) + Br2(g) ZnBr2(s) [white]
Zn(s) + I2(g) ZnI2(s) [white]


Reaction of zinc with hexacyanoferrate


Zn (II) is precipitated by potassium hexacyanoferrate ions as K2Zn[Fe(CN)6] (white precipitate)


Reaction of zinc with hydroxide ions


Elemental zinc reacts with strong bases forming hydrogen:

Zn(s) + 2 OH(aq) Zn(OH)2(s) + H2(g)

Zn2+ is precipitated by hydroxide ions as Zn(OH)2 (white amorphous precipitate) [1]

Zn2+(aq) + 2 OH(aq) Zn(OH)2(s)

By acid excess hydroxide, the precipitate is dissolved [1]

Zn(OH)2(s) + 2 H+(aq) Zn2+(aq) + 2 H2O(l)
Zn(OH)2(s) + 2 OH(aq) [Zn(OH)4]2−(aq)


Reaction of zinc with sulfide


Zn (II) is not precipitated by sulfide ions at 0.4 M HCl, but at all pH ≥ 3:

Zn2+(aq) + HS(aq) + OH(aq) ZnS(s)
[Zn(OH)4]2−(aq) + HS(aq) + 2 H+(aq) ZnS(s) + 3 H2O(l) + OH(aq)


Reaction of zinc with water


Elemental zinc will reduce steam at high temperatures [1]:

Zn(s) + H2O(g) ZnO(s) + H2(g) , ΔH = -106.4 KJ


Quantitative analysis


Method 3500-Zn C Inductively Coupled Plasma Method [2]. A portion of the sample is digested in a combination of acids. The digest is aspirated into an 8,000 K argon plasma where resulting light emission is quantified for 30 elements simultaneously.

Method limit of detection in water = 0.01 mg/L
Method limit of detection in soil = 1.00 mg/kg