C4 Redox Reactions (pg 134)

Question 1

What does Oxidation mean?

Answer 1

It can mean the addition of Oxygen (or a reaction with it) , and reduction can be the removal of oxygen.

This page we are looking at oxidation and reduction in terms of electrons

Question 2

A loss of electrons is called what?

Answer 2

Oxidation

Question 3

A gain of electrons is called what?

Answer 3

Reduction.

(a handy way to remember this is by the mnemonic OIL RIG - Oxidation Is Loss, Reduction Is Gain

Question 4

Why is it called REDOX Reactions?

Answer 4

REDuction and OXidation happen at the same time - hense the term REDOX

Question 5

Explain the Redox Reaction:

Iron Atoms are oxidised to Fe2+ ions when they react with dilute acid: Fe + 2H+ &raquo_space;> Fe2+ + H2

Answer 5

The iron atoms lose electrons. They’re oxidised by the hydrogen ions:
Fe - 2e- &raquo_space;> Fe2+

The hydrogen ions gain electrons. They’re reduced by the iron atoms: 2H+ + 2e- &raquo_space;> H2

Look at page 13 as all reactions of metals and acids on p132 are radox reactions.

Question 6

So if Electrons are transferred, is it a Redox Reaction?

Answer 6

Yes

Question 7

What is Displacement Reactions involve?

Answer 7

It involves one metal kicking another one out of a compound

The rule is:

A more reactive metal will displace a less reacive metal from its compound.

Question 8

If you put a reactive metal into a solution of a dissolved metal compound, what will happen?

Answer 8

the reactive metal will replace the less reactive metal in the compound.

(see the reactivity series on page 132).

Question 9

If you put iron in a solution of copper sulfact (CuSO4), what will happen?

Answer 9

the more reactive iron will kick out the less reactive copper from the solution. You end up with iron sulfate solution (FeSO4) and copper metal.

Iron + Copper Sulfate &raquo_space;» Iron Sulfate + copper

Fe(s) + CuSO4(aq) &raquo_space;»> FeSo4(aq) + Cu(s)

In this reaction the iron loses 2 electrons to become a 2+ ion - it’s oxidised.
The copper ion gains these 2 electrons to become a copper atom - it’s reduced

Fe &raquo_space;> Fe2+ + 2e- Cu2+ + 2e- &raquo_space;» Cu

Question 10

In displacement reactions, is it always the metal ion that gains electrons and is reduced?

Answer 10

Yes.

The metal atom always loses electrons and is oxidised.

(in your exam you could be asked to write word or symbol equations to show displacement reactions.

Question 11

What do Ionic Equations show?

Answer 11

it shows just the useful bits of reactions

In an ionic equation only the particles that react and the products they form are shown.

for example:

Mg(s) + Zn2+ (aq) &raquo_space;> Mg2+ (aq) + Zn(s)

This just shows the displacement of zinc ions by magnesium metal. Here’s what the full euation of the above reaction would be if you’d started off with zinc chloride:

Mg(s) + ZnCl2(aq) &raquo_space;> MgCl2(aq) + Zn(s)

Question 12

When you write out this equation, what can you see?

Mg(s) + Zn2+(aq) + 2Cl-(aq) &raquo_space;> Mg2+ (aq) + 2Cl-(aq) + Zn(s)

Answer 12

You can see all the ions, you’ll see that the chloride ions don’t change in the reaction - they’re spectator ions. They’re of no interest here so can be crossed out.

Instead, the ionic equation for this displacement reaction just concentrates on the substances which are oxidised or reduced.

Question 13

The equation for the reaction of zinc and iron sulface is
Zn(s) + FeSO4(aq) &raquo_space;> ZnSO4(aq) + Fe(s)

a) write an ionic equation for the reaction (1 mark)
b) state which species is being reduced and which is being oxidised (2 marks)

Answer 13

a) Zn(s) + Fe2+(aq) &raquo_space;> Fe(s) (1 mark)
b) Zn(s) is being oxidised (1 mark)
Fe2+(aq) is being reduced (1 mark)