Unit 2.3 - Metals and their Extraction

Question 1

Define an ore

Answer 1

A mineral found in the Earth’s crust that contains metal compounds, from which metals can be extracted.

Question 2

Describe the extraction methods used for metals of different reactivities.

Answer 2

Very unreactive metals (e.g. Au) are found native; more reactive metals (e.g. Al) can be extracted by electrolysis; metals in the middle of the reactivity series (e.g. Fe, Cu) can be chemically reduced with Carbon or Hydrogen.

Question 3

Describe how displacement reactions demonstrate relative reactivity of metals.

Answer 3

A more reactive metal can displace a less reactive one from its compound/salt (e.g. Fe + CuO -> FeO + Cu). If a less reactive metal is added to the salt of a more reactive metal, there will be no reaction.

Question 4

Define reduction and oxidation in terms of oxygen.

Answer 4

Reduction is the loss of oxygen, oxidation is the gain of oxygen.

Question 5

Define reduction and oxidation in terms of electrons.

Answer 5

Oxidation is loss of electrons, reduction is gain.

Question 6

Name and give the four symbol equations in the blast furnace.

Answer 6

Combustion: C + O2 -> CO2 (Then CO2 + C -> CO)
Reduction: 2Fe2O3 + 3CO -> 4Fe + 3CO2
Decomposition: CaCO3 -> CaO + CO2
Neutralisation: CaO + SiO2 -> CaSiO3

Question 7

Name the substances which are added to the blast furnace and the purpose/function of each.

Answer 7

Coke: Fuel to produce heat and reduces carbon dioxide to make carbon monoxide (a good reducing agent)
Iron(III) Oxide: Source of Iron (gets reduced to Iron)
Calcium Carbonate: Decomposes to form calcium oxide, which neutralises silicon dioxide impurities to form slag.
Hot air: Provides oxygen and heat so coke can burn.

Question 8

Name and give the four word equations in the blast furnace.

Answer 8

Combustion: Coke + Oxygen -> Carbon Dioxide (Then Carbon Dioxide + Coke -> Carbon Monoxide)
Reduction: Iron(III) Oxide + Carbon Monoxide -> Iron + Carbon Dioxide
Decomposition: Calcium Carbonate -> Calcium Oxide + Carbon Dioxide
Neutralisation: Calcium Oxide + Silicon Dioxide -> Calcium Silicate (slag)

Question 9

Why is the process in the blast furnace continuous (new raw materials added and products removed all the time)?

Answer 9

It requires a lot of energy and time to get the blast furnace up to temperature, so it is more efficient to add new products continuously and keep it at high temp.

Question 10

Why must a substance (e.g. an ionic compound like PbBr2) be liquid for electrolysis to occur?

Answer 10

Ions must be able to move to conduct electricity (and so they can move to the electrodes).

Question 11

Why is cryolite used in the extraction of aluminium?

Answer 11

Electrolysis - alumina (Aluminium oxide) must be liquid, and it dissolves in cryolite at much lower temperature than its melting point, saving energy.

Question 12

Give electrode equations for the electrolysis of aluminium oxide.

Answer 12

Al3+ + 3e- -> Al

2O2- -> O2 + 2e-

Question 13

Why must carbon electrodes used in electrolysis of aluminium be replaced regularly?

Answer 13

The oxygen formed during electrolysis reacts with the carbon electrodes to form carbon dioxide, so they must be replaced.

Question 14

Describe the properties of steel and aluminium

Answer 14

Steel - hard, strong

Aluminium - strong, low density, conducts H+E, resistant to corrosion

Question 15

Describe the properties of copper and titanium

Answer 15

Copper - very (H+E) conductive, malleable and ductile, attractive colour and lustre
Titanium - hard, strong, resistant to corrosion, high m.p and b.p.

Question 16

Name some common uses of steel and aluminium

Answer 16

Steel - high carbon = construction (strength), low carbon = car bodies (malleable), stainless steel = cutlery (no rust)
Aluminium - Overhead electricity cables, manufacturing aircraft (strong and low density)

Question 17

Name some common uses of copper and titanium

Answer 17

Copper - Water pipes (m+ductile), electrical wiring (conductive), jewellery (attractive colour)
Titanium - Drill bits (very strong), Manufacturing aircraft/spacecraft (very strong and light)

Question 18

Where are transition metals found in the periodic table?

Answer 18

In the middle of the table.

Question 19

Besides typical metal properties, what other properties do most transition metals display?

Answer 19

• Form coloured compounds and are less reactive than alkali/alkaline earth metals.
• Can form more than one type of ion (e.g. Fe2+/Fe3+).
• Many are useful catalysts (e.g. Iron in manufacturing of ammonia, platinum in cat. converters).

Question 20

Name the typical colours of copper, iron(II) and iron(III) solutions.

Answer 20

Copper - blue
Iron(II) - pale green
Iron(III) - brown

Question 21

Describe the identification of copper, iron(II) and iron (III) by their reactions with OH- ions (e.g. NaOH)

Answer 21

When dilute NaOH is added:
Copper = blue precipitate
Iron(II) = Dark/dirty green precipitate
Iron(III) = Orange/brown preciptate

Question 22

Write equation for “identification reaction” of Cu2+, Fe2+ and Fe3+ ions with NaOH

Answer 22

Cu2+ + 2OH- -> Cu(OH)2
Fe2+ + 2OH- -> Fe(OH)2
Fe3+ + 3OH- -> Fe(OH)3

Question 23

Define an alloy

Answer 23

A mixture made by mixing molten metals, whose properties can be changed depending on its composition.

Question 24

Why is steel generally more useful than iron?

Answer 24

It is much harder and stronger.