2.22-2.27 Extraction and uses of metals

Name four metal/metal compounds that the Earth’s crust contains…

1. Gold

2. Copper

3. Iron oxide

4. Aluminium oxide

What is an ore?

An ore is a metal chemically combined with other substances

What is a metal ore?

A rock that contains enough of the metal to make it worthwhile extracting

How are metals extracted from their ores? Through what processes?

Metals are extracted through electrolysis, using a blast furnace or reacting with more reactive material

What is another name for iron oxide ore?

Haematite

What is another name for aluminium oxide ore?

Bauxite

Think of two unreactive metals in the Earth’s crust:

Gold and platinum

What is the reactivity series of metals? (most to least)

1. Potassium

2. Sodium

3. Lithium

4. Calcium

5. Magnesium

6. Aluminium

7. Zinc

8. Iron

9. Copper

10. Silver

11. Gold

What three raw materials are used in a blast furnace? (Describe each)

1. Iron ore (hematite)

2. Coke (an impure form of carbon)

3. Limestone

How is the blast furnace heated up?

Hot air is blown in through the bottom

Why is limestone used in a blast furnace?

To neutralise acidic impurities

What does coke do in a blast furnace? What does it form, and how does this impact the temperature of the blast furnace?

Coke burns in hot air, forming carbon dioxide. The reaction is exothermic, heating the surface.

At higher temperatures in the furnace, what does the coke react to?

The coke reacts to carbon dioxide, reducing it to carbon monoxide

What does carbon monoxide do to the iron(III) oxide in the hematite?

Carbon monoxide reduces the iron(III) oxide in the hematite to form iron

How does limestone (calcium carbonate) reduce acidic impurities in the ore?
1. Calcium carbonate [ ] [ ] to form calcium [ ]

2. The calcium oxide reacts with the [ ] [ ], an impurity in [ ], to form calcium [ ] by neutralisation

3. This melts and collects as a molten [ ] floating on top of the molten iron

1. Calcium carbonate thermally decomposes to form calcium oxide

2. The calcium oxide reacts with the silicon dioxide, an impurity in hematite, to form calcium silicate by neutralisation

3. This melts and collects as a molten slag floating on top of the molten iron

Why is aluminium extracted from bauxite using electrolysis?

Aluminium is higher in the reactivity series than carbon

Why is aluminium oxide dissolved in molten cryolite (bauxite is purified to produce aluminium oxide first)?

Aluminium oxide has a melting point of over 2000 degrees C which would use a lot of energy and be cost-ineffective

Which metal ions collect at the cathode?

The aluminium ions - the molten aluminium is siphoned off from time to time and fresh Al₂O₃ is added to the cell

Which metal ions gather and which gas is produced at the cathode?

Oxide ions, which lose electrons (oxidation) to form oxygen

Why does the anode have to be replaced regularly (in Al₂O₃ electrolysis)?

The carbon in the graphite anodes reacts with the oxygen gas produced to produce carbon dioxide, which wears away the anode

Why is Al₂O₃ electrolysis a major expense?

A lot of electricity is required for this process

What is aluminium used in and why?

Aircraft bodies because it has a low density (and so a high strength-to-weight ratio)

Why is aluminium used for saucepans?

Very good conductor of heat and unreactive

Why is aluminium used for overhead electrical cables?

Very good conductor of electricity

hat properties make aluminium suitable for food cans?

Non-toxic, resistant to corrosion, and resistant to acidic foodstuffs

What properties make copper suitable for electrical wiring?

Very good conductor of electricity and ductile

Why is copper used for saucepans?

Very good conductor of heat, unreactive, and malleable

What properties make copper ideal for water pipes?

Unreactive (does not react with water), non-toxic, and malleable

Why is iron used as a building material?

Good strength, malleable, ductile, and relatively inexpensive

How does iron function as a catalyst?

Increases the rate of a chemical reaction without being used up (due to its variable oxidation state)

What is the composition, use, and key property of Mild Steel?

1. Iron alloyed iwht 0.25% carbon

2. Car body panels and wiring

3. Soft and malleable

What is the composition, use, and key property of High Carbon Steel?

1. Iron alloyed with 0.5–1.4% Carbon

2. Tools (for example, chisels)

3. Hard

What is the composition, uses, and key properties of Stainless Steel?

1. Iron alloyed with 20% Chromium (Cr) and 10% Nickel (Ni)

2. Cutlery, sinks, and chemical plants

3. Strong and resistant to corrosion

What does malleable mean in the context of metals?

Able to be hammered, pressed, or rolled into thin sheets without breaking

What does ductile mean in the context of metals?

Able to be drawn out into thin wires without breaking

How does carbon content affect the properties of steel?

Lower carbon content (mild steel) makes it softer and more malleable; higher carbon content makes it harder

What is an alloy?

A mixture of two or more metals or metal with a non-metal such as carbon

What is a common example of an alloy and what is it made of?

Steel, which is made from iron and carbon

Why are alloys harder than pure metals?#

• Alloys contain atoms of [ ] sizes

• This [ ] the [ ] [ ] of atoms

• So it is more [ ] for the layers of atoms to [ ] over each other

• Alloys contain atoms of different sizes

• This distorts the regular arrangements of atoms

• So it is more difficult for the layers of atoms to slide over each other