Topic 3

Question 1

What is oxidation?

Answer 1

Oxidation is the process of electron loss.

Example: Zn → Zn2+ + 2e-

Question 2

What is reduction?

Answer 2

Reduction is the process of electron gain.

Example: Cl2 + 2e- → 2Cl-

Question 3

What happens to the oxidation number during oxidation?

Answer 3

It involves an increase in oxidation number.

Question 4

What happens to the oxidation number during reduction?

Answer 4

It involves a decrease in oxidation number.

Question 5

What is the oxidation number of all uncombined elements?

Answer 5

Zero.

Question 6

How do the oxidation numbers of the elements in a compound add up?

Answer 6

They add up to zero.

Question 7

What is the oxidation number of Na in NaCl?

Answer 7

+1

Question 8

What is the oxidation number of Cl in NaCl?

Answer 8

-1

Question 9

What is the oxidation number of a monoatomic ion?

Answer 9

It is equal to its ionic charge.

Question 10

What is the oxidation number of C in CO32-?

Answer 10

+4

Question 11

What is the oxidation number of O in CO32-?

Answer 11

-2

Question 12

List some elements with invariable oxidation numbers.

Answer 12

• Group 1 metals = +1
• Group 2 metals = +2
• Al = +3
• H = +1 (except in metal hydrides where it is –1)
• F = -1
• Cl, Br, I = -1 (except in compounds with oxygen and fluorine)
• O = -2 (except in peroxides and compounds with fluorine)

Question 13

How is the oxidation number of Cl in CaCl2 determined?

Answer 13

-1

Question 14

What is the oxidation number of Fe in FeCl3?

Answer 14

+3

Question 15

How are oxidation numbers indicated in compound names?

Answer 15

By writing the number in Roman numerals.

Question 16

What is the name of FeCl2?

Answer 16

Iron (II) chloride.

Question 17

What is the name of FeCl3?

Answer 17

Iron (III) chloride.

Question 18

What is the name of NaClO?

Answer 18

Sodium chlorate(I).

Question 19

What is the name of NaNO3?

Answer 19

Sodium nitrate(V).

Question 20

What is the name of K2SO4?

Answer 20

Potassium sulfate(VI).

Question 21

What is disproportionation?

Answer 21

A reaction where an element in a single species simultaneously oxidises and reduces.

Question 22

Provide an example of disproportionation.

Answer 22

Cl2(aq) + H2O(l) → HClO(aq) + HCl(aq)

Question 23

What happens when metals react with hydrochloric acid?

Answer 23

They effervesce and dissolve, producing H2 gas.

Question 24

What is the role of an oxidising agent?

Answer 24

It causes another element to oxidise and is itself reduced.

Question 25

What is the role of a reducing agent?

Answer 25

It causes another element to reduce and is itself oxidised.

Question 26

What generally happens to metals in redox reactions?

Answer 26

They form ions by losing electrons, increasing oxidation number.

Question 27

What generally happens to non-metals in redox reactions?

Answer 27

They react by gaining electrons, decreasing oxidation number.

Question 28

What is the first step in writing half equations for redox reactions?

Answer 28

Work out oxidation numbers for the element being oxidised/reduced.

Question 29

In acidic conditions, what additional components are used in half equations?

Answer 29

H+ and H2O.

Question 30

What must be equal when combining two half equations?

Answer 30

The number of electrons.

Question 31

What is the reduction half equation for MnO4-?

Answer 31

MnO4- + 8 H+ + 5 e- → Mn2+ + 4 H2O

Question 32

What is the oxidation half equation for C2O42-?

Answer 32

C2O42- → 2 CO2 + 2 e-

Question 33

What is the result of combining the reduction and oxidation half equations?

Answer 33

A full redox equation.

Question 34

What is the oxidation half equation for I-?

Answer 34

2I- → I2 + 2 e-