Redox, Rusting And Iron

Question 1

Oxidation definition

Answer 1

Gained of oxygen, loss of hydrogen or loss of electrons

OIL

Question 2

Reduction definition

Answer 2

Reduction is loss of oxygen, gain of hydrogen or gain of electrons
RIG (Reduction is gain)

Question 3

Sulfur + Oxygen —> Sulfur dioxide

Answer 3

Sulfur is oxidised because it has gained oxygen

Question 4

2Hl —> H2 + I2

Answer 4

Oxidised because it lost hydrogen

Question 5

2Br- —> Br2 + 2e-

Answer 5

Oxidised because it has lost electrons

Question 6

N2 + 3H2 —> 2NH3

Answer 6

Reduced because it has gained hydrogen

Question 7

Rust is…

Answer 7

Hydrate iron(iii) oxide 
Fe2O3.xH2O

Question 8

What does the deliquescent chemical calcium chloride do?

Answer 8

It removes any moisture / water

Question 9

Name two other deliquescent materials

Answer 9

Calcium oxide and sodium hydroxide (solid)

Question 10

Give 5 methods used to prevent rusting and give examples of each

Answer 10

1. Barrier methods e.g painting gates chrome plating taps
2. Oil e.g bicycle chain
3. Sacrificial Protection e.g magnesium is bolted to the bottom of boats
4. Alloying e.g stainless steel which is a mixture of iron and chromium
5. Galvanising - layer of zinc

Question 11

Galvanising definition

Answer 11

Galvanising is a process that bonds a layer of zinc metal onto the surface of steel. The zinc soon reacts with the air to form zinc oxide which gives a protective layer

Question 12

Advantage of galvanising

Answer 12

Even if the zinc coating gets scratched or damaged the exposed steel will still not rust. The zinc will react instead of the iron

Question 13

Sacrificial Protection definition

Answer 13

A more reactive metal in good contact with a less reactive metal will always react first, thereby protecting the less reactive metal from corrosion

Question 14

Describe stage 1; Formation of reducing agent in the blast furnace

Answer 14

Hot air (oxygen) is blown in at the base of the furnace and coke burns to heat the furnace to 1500 degrees, forming carbon dioxide
C (s) + O2 (g) —> CO2 (g)
The carbon dioxide reacts with more coke to form carbon monoxide
CO2 (g) + C(s) —> 2CO (g)

Question 15

Describe stage 2; reduction of iron oxide to iron

Answer 15

The carbon monoxide reduces iron oxide to molten iron. Carbon monoxide is the reducing agent
3CO(g) + Fe2O3 (s) —> 3CO2 + 2Fe (l)

Question 16

Describe stage 3; removal of the impurity

Answer 16

The main impurity in iron ore is sand. The limestone added thermally decomposes to form calcium oxide
CaCO3 (s) —> CaO (s) + CO2 (g)

Calcium oxide combines with the sandy impurities (silicon dioxide) in the iron ore to form molten slag (calcium silicate)
CaO (s) + SiO2 (s) —> CaSiO3 (l)

Question 17

What is calcium silicate (slag)?

Answer 17

Slag floats on top of iron as it is less dense than iron. It is used to make roads, landfill and foundations for buildings

Question 18

How are the hot waste gases used in the blasting furnace ?

Answer 18

The gases, mainly nitrogen, carbon monoxide and carbon dioxide are used to heat up the air pumped into the bottom of the furnace, hence reducing energy costs

Question 19

What is the main impurity in crude iron?

Answer 19

Carbon (pig iron)

Question 20

How is the crude iron turned into steel ?

Answer 20

By lowering its carbon content (carbon makes iron too brittle) and adding other metals (alloy formation)

Question 21

Redox reaction

Answer 21

A redox reaction is one in which oxidation and reduction occur at the same time

Question 22

Displacement reaction definition

Answer 22

A displacement reaction is one in which a more reactive metal takes the place of a less reactive metal in a compound

Question 23

Why is rust dangerous in construction ? (2)

Answer 23

• Rust weakens the metal. Iron and steel are used extensively in construction
• so rusting is a major problem due to the cost of replacing the structures