Topic 2.1.5

Question 1

What is an oxidation number?

Answer 1

The number of electrons the atom uses to bond with any other atom

Question 2

What is the oxidation number of an uncombined element such as C, H, O2?

Answer 2

0

Question 3

What is the oxidation number of combined oxygen such as in H2O?

Answer 3

-2

Question 4

What is the oxidation number of oxygen in peroxide’s?

Answer 4

-1

Question 5

What is the oxidation number of combined hydrogen such as in NH3, H2S?

Answer 5

+1

Question 6

What is the oxidation number of combined hydrogen in metal hydrides such as LiH?

Answer 6

-1

Question 7

What is the oxidation number of a simple ion?

Answer 7

Charge on the ion
E.g. Na+—> +1
Cl - —> -1

Question 8

What is the oxidation number of combined fluorine such as NaF, CaF2?

Answer 8

-1

Question 9

When an element has more than one stable oxidation number how is it indicated?

Answer 9

Written as a Roman numeral

Question 10

What is the oxidation number of Fe in iron (III) chloride?

Answer 10

+3

Question 11

What are oxyanions?

Answer 11

Negative ions that have an element along with oxygen

Question 12

What is the oxidation number of S in
-2
SO4 ?

Answer 12

+6
Because, combined oxygen has an oxidation number of -2.
4 x -2= -8
The charge on the compound is -2. Sum of oxidation numbers must equal -2.
So, -2-(-8)= +6

Question 13

Define oxidation in terms of electron transfer and oxidation number

Answer 13

Oxidation is

• Loss of electrons
• An increase in oxidation number

Question 14

Define reduction in terms of electron transfer and oxidation number

Answer 14

Reduction is

• Gain electrons
• A decrease in oxidation number

Question 15

What is a redox reaction?

Answer 15

A reaction in which both reduction and oxidation takes place

Question 16

What is the oxidation number of a metal?

Answer 16

0, because it is an uncombined element