Extraction of Metals Flashcards
Gold, platinum and silver are unreactive. They are found in what state in the earth’s crust?
Native
What are the properties of metals?
- Strong: for construction and transport
- Malleable: easily shaped
- Ductile: drawn into wires
- Good conductors of heat
- Good conductors of electricity: power cables, electric motors
What is a metal ore?
Minerals that contain a sufficient concentration of the metal for its extraction to be economic
What is the equation for the reduction of a metal ore when it is being extracted?
M+ + e- –> M
Why must lots of energy be put in to oxide ores to extract them?
Because they are very stable
Are extraction reactions endothermic or exothermic?
Endothermic, unless a very powerful reducing agent such as aluminium metal is used
How are sulphide ores extracted?
- They are not usually reduced directly to the metals
- They are first roasted in air to produce oxides and then the oxide is reduced
- The roasting usually produced sulphur dioxide
- ZnS + O2 –> ZnO + SO2
How does sulphur dioxide dissolve in the water in clouds to form sulphurous and sulphuric acids?
SO2 (g) + H20 (l) –> H2SO3 (aq)
- Some of the sulphur dioxide is oxidised to sulphur trioxide
2SO2 (g) + O2 (g) –> 2SO3 (g) - The sulphur trioxide dissolves in water to form sulphuric acid
SO3 9g) + H20 (l) –> H2SO4 (aq)
How can we reduce the amount of acid rain produced after roasting sulphide ores?
- Any SO2 produced is collected and purified so it can be used in the manufacture of sulphuric acid
- Electrostatic precipitators are used to remove dust, after which the gas is washed with water and dried with concentrated sulphuric acid before being used in the contact process
Look over diagram showing the production of sulphuric acid.
Done!
How do we decide which method to use to extract a metal?
Based on:
- The cost of the reducing agent: C and CO are cheap and readily available, hydrogen is expensive and there is a risk of explosion, reactive metals are expensive and often extracted by electrolysis, and electricity is also expensive
- The cost of energy for the process: a high temperature means high cost, but coal is relatively cheap
- The required purity of the metal: pure iron is very soft, but alloyed with C it becomes stronger, presence of C in metals like Ti makes them brittle and of little use, Cu must be very pure for electrical wiring
Why is carbon often used as a reducing agent?
- It is cheap and plentiful
- In theory, all metal oxides can be reduced by it if the temperature is high enough
- However, temperatures over 2000 degrees C are impractical and uneconomic
What are the raw materials used in a blast furnace, in which iron is reduced by carbon?
- Iron ore: often haematite (Fe2O3)
- Coke: burns to release heat and forms the reducing agent
- Hot air: for C to burn
- Limestone: to remove acidic impurities
Look over diagram of the blast furnace
Done!
What reactions occur in the blast furnace?
- Coke burns in a blast of hot air. This is an exothermic reaction and it heats the furnace
C (s) + O2 (g) –> CO2 (g) - Carbon dioxide reacts with hot coke to form carbon monoxide gas
CO2 (g) + C (s) –> 2CO (g) - CO reduced most of the Fe2O3 at around 1200 degrees C
Fe2O3 (s) + 3CO (g) –> 2Fe (l) + 3CO2 (g) - In the hotter part of the furnace, coke also reacts directly with the Fe2O3
Fe2O3 (s) + 3C (s) –> 2Fe (l) + 3CO (g)
