Copper does not react with water, but reacts slowly with oxygen in the air to form a brownish layer of copper oxide, but unlike iron that forms rust when exposed to moist air, patina protects the copper underneath from further corrosion. A layer of patina (alkaline copper carbonate) can often be seen on copper buildings such as the Statue of Liberty [11] Copper loses its luster when exposed to sulfur due to the formation of various sulfides. [12] The oxidation states of copper are 0, +1, +2, +3 and +4, of which +1 and +2 are common oxidation states. The +3 oxidation state is potassium hexafluorocopper(III) acid, the +4 oxidation state is cesium hexafluorocopper(IV) acid, and the 0 oxidation state of Cu(CO)2 can be detected by a gas-phase reaction followed by matrix isolation [13] .
Copper is susceptible to corrosion by halogens, mutual halides, sulfur, and selenium, and vulcanized rubber can blacken copper. Copper does not react with nitrogen tetroxide at room temperature, but in the presence of nitromethane, acetonitrile, ether or ethyl acetate, copper nitrate is formed:
Cu + 2 N 2 O 4 → Cu(NO 3 ) 2 + 2 NO
Copper metal is soluble in oxidizing acids such as nitric acid, and insoluble in non-oxidizing acids if no oxidizing agent or suitable coordination reagent is present, e.g.:
The reaction between copper and nitric acid is as follows:
3 Cu + 8 HNO 3 (dilute) → 3 Cu(NO 3 ) 2 + 2 NO↑ + 4 H 2 O
Cu + 4 HNO 3 (concentrated) → Cu(NO 3 ) 2 + 2 NO 2 ↑ + 2 H 2 O
The reaction with concentrated sulfuric acid is:
Cu + 2 H 2 SO 4 (concentrated) → CuSO 4 + SO 2 ↑ + 2 H 2 O
The products of the reaction with concentrated sulfuric acid are also temperature dependent. During the reaction the sulfuric acid is gradually diluted until the reaction stops. Copper does not react with dilute sulfuric acid, but in the presence of oxygen, it reacts according to the following formula:
2 Cu + O 2 + 2 H 2 SO 4 – Δ → 2 CuSO 4 + 2 H 2 O
Copper is soluble in chloric acid or acidified chlorates:
3 Cu + 6 H + + ClO 3 – → 3 Cu 2+ + Cl – + 3 H 2 O
Coordination reaction occurs in the presence of thiourea:
2 Cu + 6 S=C(NH 2 ) 2 +2 HCl → 2Cu (I) (S=C(NH 2 ) 2 ) 3 Cl + H 2 [14]
React with concentrated hydrochloric acid to form a complex: [15]
2 Cu + 8 HCl (concentrated) → 2 H 3 [CuCl 4 ] + H 2 ↑
Copper reacts with high-Tc acid radical ions under acidic conditions, reducing the high-Tc acid radical ions to monomeric Tc:
7 Cu + 2 TcO 4 – + 16 H + → 2 Tc + 7 Cu 2+ + 8 H 2 O [16].
Copper and ferrous sulfide can undergo a replacement reaction by heating:
2 Cu + FeS → Cu 2 S + Fe
Copper can react with sulfur trioxide when heated, and there are two main reactions:
4 Cu + SO 3 → CuS + 3 CuO
Cu + SO 3 → CuO + SO 2
Copper is stable in dry air and retains its metallic luster. However, in humid air, the surface will produce a layer of copper green (alkaline copper carbonate, molecular formula: Cu 2 (OH) 2 CO 3 ), to protect the inner layer of copper is no longer oxidized. Reaction equation:
2 Cu + O 2 + CO 2 + H 2 O → Cu 2 (OH) 2 CO 3
