Using & Controlling Reactions: Metal Production

Question 1

Metals in Nature

Answer 1

= uncombined metals found naturally have low/lack of reactivity (only Ag and Au)

Question 2

Production of Metals from Ores

Answer 2

1. Extraction of Ore
   - method = open-cut or underground mining
   - product = metal ore
2. Concentration of Mineral
   - method = crushing into small particles, separate mineral from residue (froth flotation, chemical leeching)
   - product = concentrated mineral
3. Conversion of Mineral
   - method = reacting mineral with other elements (eg. O2 in roasting) into a compound suitable for reduction
   - product = compound suitable for reduction
4. Reduction of Metal
   - method = electrolysis of molten or aqueous solution
   - product = impure metal
5. Refining the Metal
   - method = further electrolysis or chemical purification
   - product = refined metal

Question 3

Production of Zinc Metal

Answer 3

1. Extraction: the ore is mined
2. Concentration
   a) the ore is crushed
   b) the ore is concentrated using froth flotation
3. Conversion
   a) the zinc sulfide concentrate is then roasted in air to form zinc oxide and sulfur dioxide *EQN
   b) the sulfur dioxide is then used to make sulfuric acid, which is then used to dissolve the zinc oxide in the next stage of the process *EQN
   c) zinc powder is added to the solution to displace any less reactive metal impurities (Ag, Cd, Cu) before the solution is electrolysed *EQN
4. Reduction: reduction of the zinc ion to zinc metal is achieved by electrolysis of the zinc sulfate solution - most energy intensive stage, because electrolyte is aqueous the energy involved is far less than that for molten.
   * EQNS

Question 4

Production of Aluminium

Answer 4

• Al very reactive therefore easily oxidised to ion but very difficult to reduce ion
• if an aq solution of Al ions is electrolysed the Al ions are not reduced at the cathode (water is reduced instead)
  therefore, production of Al requires a molten non-aqueous electrolyte.

Question 5

Reduction using Carbon

Answer 5

• metal oxides below Al on the reactivity series can be reduced with carbon
• carbon is not a very strong reducing agent, therefore cannot reduce Al2O3 to Al (or higher metals)
• Zn and Fe are below Al on the reactivity series, therefore they can be reduced with carbon

Question 6

Energy Usage in Electrolysis

Answer 6

• preferable to use an aqueous solution where possible
• a melt requires much more energy as they are IONIC substances with high MPs
• a large amount of energy is consumed to keep the electrolyte molten
• energy consumed by electrolysis of molten Al2O3 = 4x electrolysis of aqueous zinc sulfate