Reduction and electrolysis Flashcards
What is the difference between oxidation and reduction
Reduction- the gaining of electrons/ the loss of oxygen.
For example in the thermit reaction the iron is reduced
Oxidation- the loss of electrons/ the gaining of oxygen
For example in the thermit reaction the aluminium is oxidised
What are the raw materials that go in the blast furnace
Coke (carbon)- used as fuel and reacts with oxygen to form carbon monoxide
Limestone- used to remove impurities forming slag
Hot air- maintains temperature and adds oxygen
Iron ore- contains iron
The processes of the blast furnace as equations
1) carbon + oxygen —> carbon monoxide OR
2CO2 + O2 —> 2CO
2) Iron (3) oxide + carbon monoxide —> iron + carbon dioxide
OR Fe2O3 + 3CO —> 2Fe + 3CO2
3) Calcium carbonate (limestone) —> Calcium oxide + carbon
dioxide
OR CaCO3 —> CaO + CO2
4) Calcium oxide + silicon dioxide—> calcium silicate slag
Blast furnace explained
Firstly, the carbon found in the coke react with the oxygen from the air to form carbon monoxide
Secondly, the carbon monoxide reacts with the iron oxide and REDUCES it to iron metal ( carbon dioxide is also formed)
Thirdly, the limestone thermally decomposes to make calcium oxide
Fourthly, the calcium oxide reacts with sand (silicate dioxide) to form calcium silicate (slag) which is a waste product
Finally, the iron is removed from the bottom of the furnace as it is produced. New raw materials are added as the process is continuous because repeatedly heating the furnace to 1000C would be too expensive
What is electrolysis
Electrolysis is the breakdown of compounds using electricity
Happens in liquids called electrolytes (molten or dissolved compounds).
Requires two electrodes: one negatively charged (the cathode) that attracts cations (positively charged ions) and one positively charged (anode) that attracts anions ( negatively charged ions)
What occurs at the anode
Negative anions are attracted and become oxidised and they lose electrons to become neutralised.
For example,
2Cl- - 2e- –> Cl2
What occurs at the cathode
Positive Cations are attracted and are reduced when they gain electrons to become elements
For example,
Cu2+ + 2e- —> Cu
What are positive and negative charges
A positive charge is when an atom has more protons than electrons and, therefore, is not balanced as protons are positively charged.
A negative charge is when an atom has more electrons than protons and therefore, is not balanced as electrons are negatively charged.
Information of electrolysis of aluminium oxide
Requires large amounts of electricity and is very expensive ( same amount if energy needed to support a small town)
Graphite anode, oxygen formed here reacts with the carbon to make carbon dioxide which wears away the anodes so they need regular replacing.
The lining of the cell is the cathode and aluminium metal is formed here
Siting an extraction plant
Near a port to import raw materials
Away from towns and urbanisation to avoid noise pollution
Near electricity sources
Good commuting routes to town
Sustainability of metal extraction
Requires a lot of energy and greenhouse gases are released
digging up metal ores can damage the landscape
Fossil fuels and metal ores are non renewable
Better method: recycling
Less energy required (less greenhouse gases)
recycling uses 5% of the energy electrolysis uses
Less waste and can be cheaper
Describe the electrolysis process
Electrolyte is usually made from compounds dissolved in water, but this means H+ and O- ions are also present.
If the metal is more reactive than hydrogen, the hydrogen will be reduced to hydrogen gas, but if it is less reactive the metal ions will be reduced to metal.
Electrolysis of water explanation
When electricity is passed through water hydrogen and oxygen gases are made. 2x as much hydrogen is made. This means hydroxide ions are also formed instead of oxygen.
At the anode:
2OH- + 2e—> O2 + 2H+
At the Cathode
2H+ + 2e- —> H2
Electrolysis of brine and the formation of chlorine gas
When sodium chloride is dissolved in water a solution of brine is formed containing Na+, Cl-, H+ and OH- ions
The chlorine straight away goes to the anode and is oxidised into chlorine gas
2Cl + 2e- —> Cl2
The hydrogen and the sodium is attracted to the cathode but sodium is more reactive so hydrogen is reduced into hydrogen gas.
The sodium then reacts with the hydorxide left and from sodium hydroxide
this is sometimes called the CHLOROALKALI process because chlorine is formed and the alkali sodium hydroxide
