Free elements. All copper subgroup elements have position after hydrogen in the electromotive series of metals and

All copper subgroup elements have position after hydrogen in the electromotive series of metals and, therefore, don’t displace hydrogen of non-oxidant acids. The single exception is the interaction of copper with concentrated hydrochloric acid since coordination of Cu⁺ with chloride-ions in acid medium significantly decreases electrode potential to negative values:

2Cu + 4HCl = 2H[CuCl₂] + H₂

Copper readily reacts with oxidant-acids:

3Cu + 8HNO_3(dil) = 3Cu(NO₃)₂ + 2NO + 4H₂O

Cu + 2H₂SO_4(conc) = + SO₂ + 2H₂O

Ag reacts slowly with diluted and to a great extent with concentrated HNO₃:

Ag + 2HNO_3(conc) = AgNO₃ + NO₂ + H₂O

2Ag + 2H₂SO_4(conc) = Ag₂SO₄ + SO₂ + 2H₂O

Au does not react with these acids, although it is dissolved at the action of aqua regia (HCl: HNO₃ = 3: 1):

Au + 4HCl + HNO₃ = H[AuCl₄] + NO + 2H₂O

The mixture of concentrated sulfuric acid with hydrogen sulfates or sulfates of alkali metals, selenic acid, melts that contain alkalis and nitrates of alkali metals also dissolve Au(0):

Au +7H₂SeO₄ = H[Au(SeO₄)₂] +3SeO₂ + 6H₂O

2Au + 2NaOH + 3NaNO₃ = 2Na[AuO₂]+3NaNO₂ +H₂O

Gold is stable against corrosion at atmospheric conditions but the surface of copper is gradually covered by green basic carbonate:

2Cu + O₂ + H₂O + CO₂ (CuOH)₂CO₃;

Silver is coated by black film of silver sulfide, Ag₂S:

4Ag + O₂ + 2H₂S 2Ag₂S + H₂O.

It is worth to note that Ag inactive to oxygen attack at the absence of H₂S. Oxide film does not exist at the surface of silver and gold. Thus, the latter reaction takes place namely due to the formation of virtually insoluble compound, Ag₂S (the solubility of silver sulfide, Ag₂S, in water is 2.83×10^-15 g/L, K_SP (Ag₂S) = 6×10^–51).

It is only metal copper in the subgroup that reacts with oxygen:

2Cu + O₂ = 2CuO

Copper monoxide decomposes at t^o > 800°С:

4CuO = 2Cu₂O + O₂

Oxides of Ag and Au can be prepared indirectly.

Free metals react with chlorine and fluorine:

Cu + Cl₂ = CuCl₂

2Ag + Cl₂ = 2AgCl

2Au + 3Cl₂ = 2AuCl₃

Дата добавления: 2015-07-25