1.7 Redox

Question 1

What is oxidation in term of electrons?

Answer 1

Oxidation is the process of electron loss.

It involves an increase in oxidation number.

Question 2

What is reduction in term of electrons?

Answer 2

Reduction is the process of electron gain.

It involves a decrease in oxidation number.

Question 3

What are the 5 rules for assigning oxidation numbers?

Answer 3

1. All uncombined elements have an oxidation number of zero.
2. The oxidation numbers of the elements in a compound add up to zero.
3. The oxidation number of a monoatomic ion is equal to the ionic charge.
4. In a polyatomic ion (C(O3)2-) the sum of the individual oxidation numbers of the elements add up to the charge on the ion.
5. Several elements have invariable oxidation numbers in their common compounds.

Question 4

What oxidation number is assigned to group 1 metals?

Answer 4

+1

Question 5

What oxidation number is assigned to group 2 metals?

Answer 5

+2

Question 6

What oxidation number is assigned to Al?

Answer 6

+3

Question 7

What oxidation number is assigned to H?

Answer 7

+1

except in metal hydrides where it is -1 , e.g. NaH

Question 8

What oxidation number is assigned to F?

Answer 8

-1

Question 9

What oxidation number is assigned to Cl, Br, I?

Answer 9

-1

except in compounds with oxygen and fluorine.

Question 10

What oxidation number is assigned to O?

Answer 10

-2

except in peroxides (H2O2) where it is -1 and in compounds with fluorine

Question 11

What is the oxidation number of Fe in FeCl3?

Answer 11

+3

see page 1 in the chemrevise revision guide for an explanation

Question 12

What is the oxidation number of Cl in CaCl2?

Answer 12

-1

see page 1 in the chemrevise revision guide for an explanation

Question 13

What is an oxidising agent?

Answer 13

An electron accepter.

The species that causes another element to oxidise.

It is itself reduced in the reaction.

Question 14

What is an reducing agent?

Answer 14

An electron donor.

The species that causes another element to redusce.

It is itself oxidised in the reaction.

Question 15

Which is the oxidising and reducing agent in the equation:

Br2(aq) + 2I-(aq) -> I2(aq) + 2Br-(aq)

Draw the half equation for Br and I in this reaction.

Answer 15

Br - oxidising agent
I - reducing agent

(see page 1 in the chemrevise revision guide)

Question 16

Answer example labelled 1 on page 2 in the chemrevise revision guide.

Answer 16

correct?

Question 17

Answer example labelled 2 on page 2 in the chemrevise revision guide.

Answer 17

correct?