Redox reactions

Question 1

Redox is a word made up from two processes that work together.

Answer 1

The two processes are reduction and oxidation.

Question 2

Rusting is a redox reaction:

Answer 2

iron + oxygen + water ⇒ hydrated iron(III) oxide

Question 3

What does galvanising do?

Answer 3

• Galvanising protects iron from rusting by covering it with a layer of zinc.
• The layer of zinc stops water and oxygen from reaching the surface of the iron.
• Zinc also acts as a sacrificial metal, as it is more reactive than iron.

Question 4

Oxidation and reduction can also be described in terms of electrons.

Answer 4

• A substance is oxidised if it loses electrons. An oxidizing agent takes electrons away from a substance.
• A substance is reduced if it gains electrons. A reducing agent pushes electrons onto anothera substance so that it gains electrons.

Question 5

What happens during rusting?

Answer 5

• When iron rust, the oxygen is the oxidizing agent; it takes electrons from the iron. The electrons go into the oxygen, so the oxygen itself is reduced.
• Iron loses electrons - it is oxidised.
• Oxygen gains electrons - it is reduced.

Question 6

Redox reactions can be forced to either direction.

Answer 6

• One direction is oxidation; the other is reduction.
• ​Iron is normally oxidised, but it can be pushed back.
• Iron ions can be forced from one type to another.
• Chlorine is like oxygen in that it is normally reduced.

Question 7

Oxidation of Fe

Answer 7

Fe²⁺ + 2e^-

Question 8

Reduction of Fe²⁺

Answer 8

Fe

Question 9

Oxidation of Fe²⁺

Answer 9

Fe³⁺ + e^-

Question 10

Reductio of Fe³⁺

Answer 10

Fe²⁺

Question 11

Reduction of Cl₂

Answer 11

2Cl^-

Question 12

Oxidation of 2Cl^-

Answer 12

Cl₂ + 2e^-

Question 13

When a word equation for a displacement reaction is written

Answer 13

• The more reactive metal ‘swaps places’ with the less reactive metal. For example: magnesium is more reactive than zinc, so zinc is replaced.
• Magnesium + zinc sulfate ⇒ magnesium sulfate + zinc

Question 14

The order of reactivity is needed to work out displacement reactions:

Answer 14

• Magnesium, zinc, iron, tin.
• This means that magnesium displaces zinc, iron, and tin.
• Zinc displaces iron and tin.
• Iron displaces tin.

Question 15

Displacement happens with

Answer 15

Reactive metals and compounds of a less reactive metal.

Question 16

How do metals react?

Answer 16

• All metals react by pushing off electrons and turning into ions. This is oxidation.
• These electrons are forced onto the ions of other metals that are not so reactive.
• Metal atoms that gain these electrons are reduced.

Question 17

Symbol equation for displacement reaction for magnesium and zinc sulfate

Answer 17

Mg + ZnSO₄ ⇒ MgSO₄ + Zn

Question 18

Ionic equation for displacement reaction for magnesium and zinc sulfate

Answer 18

Mg + Zn²⁺ ⇒ Mg²⁺ +Zn

Question 19

Tin Barrier

Answer 19

Iron coated with tin which acts as a barrier. It is less reactive so loses electrons even faster causing rusting.

Question 20

Sacrificial Protection

Answer 20

Iron can be coated in a thin layer of zinc or magnesium. Zinc and magnesium more reactive than iron, so lose electrons in preference to iron. These are sacrificial metals and the process is called sacrificial protection