Unit 13 Flashcards
Metal ores
Sodium =
Rock salt
Metal ores
Aluminium =
Bauxite
Metal ores
Iron = hematite
Method of extraction
Potassium, k. Most reactive
Sodium, na Ores more difficult to
Calcium, ca Decompose
Magnesium, mg More expensive
Aluminium , al More difficult
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Carbon
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Zinc, zn Heating with a reducing agent
Iron, fe (Carbon or carbon monoxide)
Lead, pb
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Hydrogen
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Copper, cu Occur naturally as elements
Silver, ag So no chemical reaction is needed
Gold, au Only separation from impurities
Extraction of zinc from zinc blend
Zinc is mainly zinc sulphide, ZnS. First it is roasted in air, giving zinc oxide
Zinc sulphide + oxygen –> zinc oxide + sulphur dioxide
2ZnS + 3O –> 2ZnO + 2SO2
Then the oxide is reduced in one of the two ways below:
1. Using carbon monoxide. This is carried in a furnace:
Zinc oxide + carbon monoxide –> zinc + carbon dioxide
ZnO + CO –> Zn + CO2
The final mixture contains zinc and a slag of impurities. The zinc is separated from it by fractional distillation
- Electrolysis
Extraction of iron
A mixture called the charge, containing the iron ore, is added through the top of the furnace. Hot air is blasted in through the bottom. After a series of reactions, liquid iron collects at the bottom of the furnace
The charge contains three things
- Iron ore.
- Limestone
- Coke
The reactions in a blast furnace
Stage 1: the coke burns giving off heat
The blast of hot air starts the coke burning. It reacts with the oxygen in the air, giving carbon dioxide:
Carbon + oxygen–> carbon dioxide
C + 02 = CO2
It’s a combustion reaction which means it’s a redox reaction. The carbon is oxidised to carbon dioxide. The blast of air provides the oxygen for the reaction.
The reaction is exothermic - it gives off heat , which helps to heat the furnace
The reactions In the blast furnace
Stage 2: carbon monoxide is made
The carbon dioxide reacts with more coke, giving carbon monoxide:
Carbon + carbon monoxide –> carbon monoxide
C + CO2 = 2CO
In this redox reaction, the carbon loses oxygen. It is reduced
The reaction is endothermic- it takes in heat from the furnace. This is good because stage 3 needs a lower temperature
The reaction in the blast furnace
Stage 3: the iron (111) oxide is reduced
This is where the actual extraction occurs. Carbon monoxide reacts with the iron ore giving liquid iron
Iron + carbon monoxide –> iron + carbon dioxide
Fe2O3 + 3CO –> 2Fe + 3CO2
The iron trickles to the bottom of the furnace
In this redox reaction, carbon monoxide acts as the reducing agent. It reduces the iron (111) oxide to the metal
At the same time the carbon monoxide is oxidised to carbon dioxide
What is limestone used for?
The limestone reacts with the sand (silica) in the ore, to form calcium silicate or slag
Limestone + silica –> calcium silicate + carbon dioxide
CaCO3 + SiO2,–> CaSiO3 + CO2
The slag runs down the furnace and floats on the iron
The purpose of this reaction is to remove impurities from the molten iron
Silica is an acidic oxide . It’s reaction with limestone is neutralisation (because limestone is a base) giving calcium silicate , a salt
Waste gases
Carbon dioxide and nitrogen. They come out the top of the furnace
The carbon dioxide is from the reduction in stage 3. The nitrogen is from the air blast. It has taken part in the reactions so has not been changed
The molten iron is tapped from the bottom. It is impure with carbon as the main impurity . Some is run into moulds to give cast iron this is hard but brittle. But most of the iron is turned into steel
Use of aluminium and what properties make it useful
Overhead electricity cables (w steel core for strenghth) , coating DVDs and cds, cooking foil and food cartons , drink cans
Good conductor of electricity, ductile , resists erosion, non toxic, shiny service that reflects the laser beams that reads cds and dvds, can be rolled into thin sheets
Uses for copper and what properties make it useful
Electrical wiring , roofing , saucepan bases
One of the best conductors of electricity, ductile , malleable , develops an attractive protective coating conducts heat well , unreactive , tough
Uses for lead and what properties make it useful
Holding the glass in stained glass windows, and sealing joins in roofs car batteries
Easy to bend at room temp , unreactive
Gives a current when connected to lead oxide in an electrolyte (dilute sulphuric acid)
Uses of zinc and what properties make it useful
Protecting steel from rusting coating or galvanising iron and steel for torch batteries
Offers sacrificial protection if coating cracks gives a current when connected to a carbon electrode, in an electrolyte
Uses of silver and what properties make it useful
Electrical connections inside mobile phones, keyboards, and photovoltaic (PV) cells mirrors , and mirrored sunglasses jewellery
The best metal of all at conducting electricity, ductile.
Reflects light very well, even in a very thin coat looks good, and resists corrosion
Uses of titanium and what properties make it useful
Tooth implants, and replacement hip and knee joints. Exhaust pipes for planes pipes and tanks in chemical factories
What is an alloy
A mixture of metals that changes there properties or increase them. Turing a metal into an alloy increases its range of uses
How to make mild steel
When Carbon (0.5%) is mixed with pure iron the result is mild steel
What are the uses of mild steel
Building, ships , car bodies and machinery
How to make stainless steel
When nickel and chromium are mixed with iron, the result is stainless steel. This Is hard and rustproof
Uses of stainless steel
Car parts, kitchen sinks and cutlery
Atoms in a pure metal
They are arranged in a regular lattice. (In fact they are metal ions) in a sea of electrons)
When pressure is applied to a metal, for example by hammering the metal
The layers can slide over each other easily. That is why a metal is malleable and ductile
Structure when the metal turns to an alloy
New atoms enter the lattice. The layers can no longer slide easily. So the alloy is stronger than the original metal
The first stage of making steels
Unwanted impurities are removed from the iron
The molten iron from the blast furnace is poured into an oxygen furnace. Calcium oxide is added, and a jet of oxygen is turned on. The calcium oxide neutralises any acidic impurities, forming a slag that is skimmed off. The oxygen reacts with the other burning them away
The second stage of making steels
Then other elements may be added
This is measured out carefully, to give steels with the required properties
What is the alloy stainless steel made up of
70% iron
20% chromium
10% nickel
Special properties of a stainless steel
Does not rust
Uses of stainless steel
Car parts, kitchen sinks, cutlery, tanks and pipes in chemical factories, surgical instruments
What is aluminium (alloy number 7075 TF) made from
90.25% aluminium
6% zinc
2.5% magnesium
1.25% copper
What are the properties of aluminium (alloy number 7975 TF)
Light but very strong
Uses of aluminium (7075 TF)
Aircraft
What is brass made from
70% copper
30% zinc
What are brass’ special properties
Harder than copper, does not corrode
What are the uses of brass
Musial instruments, ornaments, door knobs and other fittings
What is bronze made of
95% copper
5% tin
Special properties of bronze
Harder than brass, does not corrode, chimes when struck
Uses of bronze
Statues, ornaments, church bells
Why have hundreds of aluminium alloys been made?
Aircrafts need materials that are light but very strong , and resistant to corrosion. Pure aluminium is light , but not strong enough. So hundreds of aluminium alloys have Been developed, for aircraft parts
What is corrosion
When a metal is attacked by air, water or other substances in its surrounding is said to make a metal corrode
The more reactive a metal is, the more readily it corrodes
What does rusting involve
Rusting needs both air and water.
The chemical equation for how iron is oxidised.
4Fe. +. 302 + 2H20. —> 2Fe2O3H2O
Iron + oxygen + water —> hydrated iron(111) oxide(or rust)
How to prevent rusting
- Coat the metal with something to keep the air and moisture out.
Paint
Grease
Plastics
Another metal
What is galvanizing
By dipping iron into molten zinc
What is the process of tin plating
Deposited on the steel by electrolysis
How to prevent rusting with chromium
Coating with chromium. The chromium is deposited by electrolysis
Using sacrificial protection to prevent rusting
This is when a more reactive metal is attached to the metal and it corrodes instead of the steel.
Does aluminium corrode?
No, because a coat of aluminium oxide forms on the aluminium which acts as a seal preventing corrosion
