Zinc

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)

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]

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)

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

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

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

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)

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)

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

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

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