Chapter 16 - (Extraction & corrosion of metals) Flashcards
What does the earth’s crust contain?
metal compounds such as gold, copper, Iron oxide, aluminum oxide.
What happens to useful metals?
Chemically combined to form ores
By which process are metals extracted through their ores?
Process such as electrolysis - using a blast furnace or by reacting with more reactive material.
How does metal become an oxide in extraction?
The extraction of these metals is a reduction process since oxygen is being removed.
What are common examples of oxides ores?
Iron, and aluminum ores which are called hematite and bauxite respectively
Can unreactive metals be extracted chemically?
No, they are found as the uncombined element.
- do not react with other substances due to their chemical stability
What are unreactive metals known as and what are the examples?
Native metals, examples - gold and platinum which is mined directly from the Earth’s crest.
What does the extraction method depend on?
Position of metals in the reactivity series.
Which method does, Potassium, Sodium, Lithium, Calcium, magnesium and aluminum use?
- Extracted by electrolysis of the molten chloride or molten oxide
- Large amount of electricity required so expensive process
Which method does zinc, iron, hydrogen, copper, silver, and gold use?
- extracted by heating with a reducing gent such as carbon monoxide in a blast furnace.
- Cheap process as carbon is cheap and can be source of heat as well.
- found as pure element
how is iron extracted?
- From a large container called a blast furnace from it’s ore, hematite
- moder blast furnaces produce 100, 000 tonnes of iron
How does extraction of iron from hematite start?
- Raw materials: Iron ore (hematite), coke (an impure form of carbon), and limestones are added into the top of the blast furnace.
- hot air is blown into the bottom.
What happens in zone 1 of extraction of iron from hematite?
- coke burns in hot air forming carbon dioxide.
- reaction is exothermic so it gives off heat, heating the furnace.
Carbon + oxygen –> carbon dioxide
What happens in zone 2 of extraction of iron from hematite?
- at High temperatures in the furnace, more coke reacts with CO2 forming carbon monoxide.
- carbon dioxide has been reduced to carbon monoxide
Carbon + carbon dioxide —> carbon monoxide
What happens in zone 3 of extraction of iron from hematite?
- carbon monoxide reduces iron (III) oxide in iron ore to form iron.
- melts and collects at the bottom of the furnace,
Iron (III) oxide + carbon monoxide –> carbon dioxide
- limestone (calcium carbonate) is added to the furnace to remove impurities in ore.
- calcium carbonate in limestone thermally decomposes to form calcium oxide.
Calcium carbonate –> calcium oxide + carbon dioxide
- calcium oxide reacts with silicon dioxide, which is an impurity in iron ore to form calcium silicate
- melts and collects as a molten slag floating on top of molten iron
Calcium oxide + silicon dioxide –> calcium silicate
What is the symbol equation in Zone 1: The burning of carbon (coke) to provide heat and produce carbon dioxide?
C (s) + O2 (g) –> CO2 (g)
What is the symbol equation in Zone 2: Reduction of carbon dioxide to carbon monoxide?
CO2 (g) + C (s) –> 2CO (g)
What is the symbol equation in zone 3: The reduction of iron (III) oxide by carbon monoxide?
Fe2O3 (s) + 3CO2 (g) —> 2Fe (l) + 3CO2 (g)
What is the symbol equation in zone 3: The thermal decomposition of calcium carbonate (limestone) to produce calcium oxide?
CaCO3 (s) –> CaO (s) + CO2 (g)
What is the symbol equation in zone 3: The formation of slag?
CaO (s) + SiO2 (s) –> CaSiO3 (l)
What is aluminum’s ore?
bauxite
Why can aluminum not be extracted by reduction using carbon?
Higher in reactivity series than carbon
How is aluminum extracted?
electrolysis
What happens to the bauxite First in the process of aluminum extraction by electrolysis?
purified to produce aluminum oxide Al2O3.
What happens to the aluminum oxide in the process of aluminum extraction by electrolysis?
dissolve in molten cryolite
Why is aluminum oxide dissolved in molten cryolite in the process of aluminum extraction by electrolysis?
- Aluminum oxide has a melting point of over 2000°C which uses a lot of energy and is very expensive.
- Resulting mixture has a lower melting point, without interfering with reaction.
what happens to the aluminum oxide dissolved in molten cryolite in the process of aluminum extraction by electrolysis?
- Mixture is placed in an electrolysis cell, made from steel, lined with graphite
- Graphite lining acts as the negative electrode, with several large graphite blocks as the positive electrode.
what happens at the cathode (negative electrode) in the process of aluminum extraction by electrolysis?
- Aluminum ions gains electrons (reduction)
- Molten aluminum forms at the bottom of the cell
- The molten aluminum is siphoned off from time to time and fresh aluminum oxide is added to the cell
Al 3+ + 3e- –> Al
what happens at the anode (positive electrode) in the process of aluminum extraction by electrolysis?
- oxide ions lose electrons (oxidation)
- oxidation is produced at the anode:
2O 2- –> O2 + 4e-
Overall equation:
2Al2O3 –> 4Al + 3O2
- carbon in the graphite anodes reacts with the oxygen produced to give CO2.
C (s) + O2 (g) –> CO2 (g)
- anode wears away and has to be replaced regularly
what is required in the process of aluminum extraction by electrolysis?
a lot of electricity is required for this process and causes major expenses
