10: Occurrence and Extraction of Metals

Question 1

What is the most abundant element by mass in the Earth’s crust?

Answer 1

Oxygen (49.2%)

Question 2

What is the most abundant metal by mass in the Earth’s crust?

Answer 2

Aluminium (7.5%)

Question 3

What are ores?

Answer 3

Ores are rocks containing minerals in concentrations that are high enough for economical extraction.

Question 4

Name 2 oxide ores and the names of metal compounds found in these ores.

Answer 4

Bauxite: hydrated aluminium oxide Haematite: iron(III) oxide

Question 5

What is the chemical formula of hydrated aluminium oxide?

Answer 5

Al₂O₃·2H₂O

Question 6

What is the chemical formula of iron(III) oxide?

Answer 6

Fe₂O₃

Question 7

Name 4 sulphide ores and the names of metal compounds found in these ores.

Answer 7

Copper pyrite: copper(II) iron(II) sulphide
Cinnabar: mercury(II) sulphide
Galena: lead(II) sulphide
Zinc blende: zinc sulphide

Question 8

What is the chemical formula of copper pyrite?

Answer 8

CuFeS₂

Question 9

What is the chemical formula of mercury(II) sulphide?

Answer 9

HgS

Question 10

What is the chemical formula of lead(II) sulphide?

Answer 10

PbS

Question 11

What is the chemical formula of zinc sulphide?

Answer 11

ZnS

Question 12

Name three carbonate ores and the names of metal compounds found in these ores.

Answer 12

Calamine: zinc carbonate
Magnesite: magnesium carbonate
Malachite: copper(II) carbonate

Question 13

What is the chemical formula of zinc carbonate?

Answer 13

ZnCO₃

Question 14

What is the chemical formula of magnesium carbonate?

Answer 14

MgCO₃

Question 15

Name one halide ore and the metal compound found inside.

Answer 15

Rock salt: sodium chloride

Question 16

What is roasting and which type of metal compound is it applicable to?

Answer 16

Roasting refers to the process of heating the concentrated ore strongly in the presence of excess air. It is commonly used for sulphide ores to convert them into oxide ores.

Question 17

What is calcination and which type of metal compound is it applicable to?

Answer 17

Calcination refers to the process of heating the concentrated ore strongly in the without / with a limited supply of air. It is commonly used for carbonate ores to convert them into oxide ores.

Question 18

List three methods metals can be extracted from their oxides.

Answer 18

by heating alone, by (carbon / carbon monoxide) reduction, by electrolysis

Question 19

Which additional substance is used in the extraction of aluminium and why?

Answer 19

Cryolite is added to lower the melting point of aluminium as lower operation costs are needed for less heat energy.

Question 20

Why does bauxite have to be molten in order for electrolysis to take place?

Answer 20

Since the ore must be molten for ions to move freely, the ore must be heated to melt.

Question 21

List three reasons why the material of the electrode used in extraction of aluminium is chosen.

Answer 21

The material is graphite.
1. It conducts electricity.
2. It has a high melting and boiling point.
3. It is chemically inert.

Question 22

Do electrodes involved in the extraction of aluminium need to be replaced regularly?

Answer 22

The positive electrode does. This is because at the positive electrode, oxygen ions are attracted and form oxygen atoms, which oxidises carbon in high temperature to become carbon dioxide.

Question 23

Can carbon electrodes be made of diamond instead?

Answer 23

No, because diamond has a giant covalent structure in which no delocalised electrons can be found, so it cannot conduct electricity.

Question 24

Why do aluminium ions and oxygen ions break the octet rule to form aluminium atoms and oxygen atoms in electrolysis?

Answer 24

The presence of electrical energy forces the ions to break the octet rule.

Question 25

What is the name of the equipment used to extract iron industrially?

Answer 25

Blast furnace

Question 26

What materials are added to the blast furnace for the extraction of iron?

Answer 26

1. iron ore, such as haematite, containing iron(III) oxide 2. coke (**carbon**) 3. **limestone**, which is used to purify the iron.

Question 27

How is iron extracted industrially?

Answer 27

1. Hot air is shot at the bottom of the furnace. 2. Coke (carbon) reacts with hot oxygen to form carbon dioxide. 3. Carbon dioxide rises and reacts with hot carbon to form carbon monoxide. 4. Carbon monoxide reduces iron(III) oxide back to iron. (carbon monoxide + iron(III) oxide -> iron + carbon dioxide) 5. The high temperature decomposes calcium carbonate to calcium oxide and carbon dioxide. 6. Calcium oxide reacts with impurities (silicon dioxide) to form calcium silicate, which runs down to form the slag.

Question 28

Is the year of discovery of the metals related to the abundance of the metals?

Answer 28

No, it is related to the **reactivity**, since higher technology is required to extract more reactive metals.

Question 29

How does recycling aluminium help save energy?

Answer 29

Aluminium is extracted from molten aluminium oxide at **high temperatures** by **electrolysis**. The process requires huge amounts of **electrical energy**. Therefore, recycling saves energy, since recycling aluminium does not involve electrolysis.