Copper and its compounds (A-level inorganic chemistry)
Copper and its compounds
The electron configuration of copper
[Ar]4s13d10
Properties of copper as a transition element
- Forms colored compounds; for instance Cu2+ is blue
- Has variable oxidation states; +1, +2,
- Forms complexes, e.g. Cu(NH3)42+.
- CuSO4 is a catalyst in preparation of hydrogen from dil. sulphuric acid
Trial 1
(i) Write the electron configuration of copper. (01mark)
(ii) State properties which show copper as a d-block element. (01mark)
Properties and uses of copper
Copper has a melting point of 10830C and a density of 8.94 g cm-3. It is a tough, malleable and ductile metal with an attractive golden color. It has electrical and thermal conductivity, thus used for electric cables and calorimetres.
Extraction of copper
pyrites, CuFeS2,
copper glance, CuS,
cuprite, Cu2O.
Extraction of copper from pyrites
1. The concentration of the ore by floatation method
(i) The finely pulverized ore is mixed with water, containing ‘frothing’ agent (s).
(ii) Air is blown into the mixture, froth is produced and the earthly material is “wetted” and sinks.
(iii) The sulphide ore particles, rise to the surface in the froth and are skimmed off the surface.
(iv) Anti- frothing agent is added to break up the froth, the concentrated ore is filtered and dried.
2. Roasting
The ore is then roasted in a limited supply of air to convert the iron into iron (II) oxide.
2CuFeS2 (s) + 4O2 (g) → Cu2S (s) + 3SO2 (g) + 2FeO (s)
3. Addition of SiO2 to remove impurities
Silica, SiO2, is added to the mixture and heated in the absence of air to convert the iron (II) oxide into a slag of iron (II) silicate, FeSiO3, which is poured away.
FeO(s) + SiO2 → FeSiO3(s) (slag)
4. Conversion of copper sulphide to copper
The copper (I) sulphide is reduced to copper by heating in a controlled amount of air.
Cu2S (s) + O2 (g) → 2Cu (s) + SO2 (g)
5. Purification of copper by electrolysis
Anode: Impure copper: Cu(s) – 2e → Cu2+ (aq)
Cathode; pure copper strip: Cu2+(aq) + 2e → Cu(s)
Electrolyte: Copper sulphate
Trial 1
(a) Write the formulae of two ores of copper. (1 marks)
(b) Suggest one method by which the ores may be concentrated. (1 marks)
(c) Outline, giving equations, the process by which impure copper is obtained from the concentrated ore. (6 marks)
(i) Name the method by which impure copper is purified. (1 mark)
(ii) Describe, giving equations the process of purification of copper in (i) above. (4 marks)
(iii) Give two large scale uses of copper (1 mark)
(c) 6.53 g of impure copper dissolved in excess nitric acid. The solution obtained was made up to 250cm3 of solution with water. To 25 cm3 of this solution excess aqueous potassium iodide was added. The reaction that took place is given by the equation
2Cu2+(aq) + 4I– (aq) → Cu2I2(s) + I2(aq)
The iodine liberated reacted with 20 cm3 of 0.5 M aqueous sodium thiosulphate according to the equation
I2(aq) + 2S2O32-(aq) → S4O62-(aq) + 2I–(aq)
Calculate the percentage by mass the purity of copper in the sample (Cu=64) (6 marks)
Trial 2
In the extraction of copper from its ore, the ores are first concentrated and then roasted in air. The roasted material is then mixed with silica and heated by hot air in a blast furnace producing copper.
(i) Write the formula of one ore from which copper can be extracted. ( ½ mark)
(ii) Describe the process by which the ore named in (a) can be concentrated. (4 marks)
(iii) Write an equation for the reaction that takes place when the ore is roasted in air. (1½ marks)
(iv) Write an equation for the reaction that leads to the formation of copper. (3 marks)
The reaction of copper with water
Copper does not react with water or steam
The reaction of copper with sodium hydroxide
Copper does not react with sodium hydroxide
The reaction of copper with hydrochloric acid
Copper does not react with dilute hydrochloric acid
It reacts with concentrated hydrochloric acid liberating hydrogen
2Cu(s) + 4HCl(aq) → H2CuCl4(aq) + H2(g)
The reaction of copper with sulphuric acid
Copper does not react with dilute sulphuric acid
It reacts concentrated sulphuric acid to give copper sulphate, sulpur dioxide, and water
Cu (s) + 2H2SO4 (aq) → CuSO4 (aq) + SO2 (g) + 2H2O (l)
The reaction of copper with nitric acid
Copper does not react with very dilute nitric acid
With 50% nitric acid it forms copper nitrate, nitrogen monoxide, and water.
3Cu (s) + 8HNO3 (l) → 3Cu(NO3)2 (aq) + 4H2O (l) + 2NO (g)
Copper reacts with concentrated nitric acid to form copper nitrate, nitrogen dioxide and water
Cu (s) + 4HNO3 (l) → Cu(NO3)2 (aq) + 2H2O (l) + 2NO2 (g)
Trial 3
State the conditions under which copper reacts with the following acids and in each case write an equation for the reaction:
(i) Sulphuric acid (3 marks)
(ii) Nitric acid (3 marks)
(iii) hydrochloric acid (3marks)
Trial 4
State what would be observed and write equations for the reactions which take place when the following reagents are added dropwise to a solution of copper (II) sulphate until in excess;
- (i) Concentrated hydrochloric acid. (3 marks)
- (ii) Sodium hydroxide solution. (2 marks)
Qualitative analysis of copper II ions
The reaction of copper ions with sodium hydroxide solution
Forms a blue precipitate insoluble in excess
Cu2+(aq) + 2OH– (aq) → Cu(OH)2(s)
The reaction of copper with an ammonia solution
Forms a blue precipitate soluble in excess to form a deep blue solution
Cu2+(aq) + 2OH– (aq) → Cu(OH)2(s)
Then,
Cu(OH)2(s) + 4NH3(aq) → Cu(NH3)42+(aq) + 2OH–(aq)
The reaction of copper ions with a potassium iodide solution
Forms a white precipitate and brown solution
2Cu2+(aq) + 2I– (aq) → 2CuI(s) + I2(aq)
Reaction of copper (II) ions with potassium hexacyanoferrate II solution
Brown precipitates is formed
Cu2+ (q) + Fe(CN)64- (aq) → Cu2Fe(CN)6
The reaction of copper (II) with concentrated hydrochloric acid
The color of the solution turns from blue to green to yellow.
[Cu(H2O)6]2+(aq) + 4Cl–(aq) → [CuCl4]2-(aq) + 6H2O(l)
Blue green/yellow
Trial 5
Explain the following observation;
(a) To a dilute solution of copper (II) sulphate was added concentrated hydrochloric acid dropwise until in excess. A student wrote the following equation for the reaction that took place.
CuSO4(aq) + 2HCl (aq) → CuCl2(aq) + H2SO4(aq)
Explain what is wrong with the equation. (4 marks)
Trial 6
Copper (II) chloride dissolves in concentrated hydrochloric acid to form a brownish yellow solution; which on dilution with water turns green-blue and finally pale blue. Explain the statement.
Trial 7
To an aqueous solution of copper (II) sulphate was added concentrated hydrochloric acid dropwise until in excess.
Name the copper species present in the solution before hydrochloric acid was added. (1 mark)
Write the formula of the copper species in the solution, containing excess hydrochloric acid.
The solution containing excess hydrochloric acid was diluted with water.
State the color changes that took place. (1 mark)
Write an equation for the reaction that took place. (2 marks)
Trial 8
A green powder was dissolved in dilute hydrochloric acid to form a green solution. The solution was divided into three parts.
(a) To the first portion of the solution was added a few drops of potassium hexacyanoferrate (II) solution. A brown precipitate was formed.
(i) Name the cation in the powder. (1 mark)
(ii) To the second portion of the solution was added concentrated hydrochloric acid drop wise until in excess;
(b) State what was observed;
(i) Write an equation for the reaction that took place. (1½ marks)
(ii) Magnesium powder was added to the third portion of the solution and the mixture warmed. State what was observed.
(v) Write an equation for the reaction that took place. (1½ marks)
Suggested
Trial 1
%Cu = 24.5%
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