Redox reactions

Question 1

In terms of electron transfer what does reduction mean?

Answer 1

The gaining of electrons

Question 2

In terms of electron transfer what does oxidation mean?

Answer 2

The loss of electrons

Question 3

Define oxidising agent

Answer 3

A reagent that removes electrons from another species

Question 4

Define reducing agent

Answer 4

A reagent that adds electrons to another species

Question 5

Define oxidation number

Answer 5

A measure of the number of electrons that an atom uses to bond with atoms of another element

Question 6

What is the oxidation number of uncombined atoms?

Answer 6

0

Question 7

What is the oxidation number of:

i) Group 1 elements
ii) Group 2 elements

Answer 7

i) +1

ii) +2

Question 8

What is the oxidation number of fluorine atoms?

Answer 8

-1

Question 9

Oxygen has an oxidation number of -2, apart from when it is in what? What does the oxidation number change to in that situation?

Answer 9

Except when oxygen is in a peroxide when the oxidation number is -1

Question 10

i) What is the oxidation number of hydrogen usually?

ii) In what situation is it -1?

Answer 10

i) +1

ii) When it is a hydride (E.g. LiH)

Question 11

How are oxidation numbers represented when naming a compound?

Answer 11

Roman numerals in brackets E.g. copper (II) nitrate (V)

Question 12

Define oxidation in terms of oxidation number

Answer 12

The oxidation number becomes more positive

Question 13

Define reduction in terms of oxidation number

Answer 13

The oxidation becomes more negative

Question 14

What is oxidised and reduced in each of the following reactions?

i) Mg + H2SO4 —>MgSO4 + H2
ii) CaCO3 + 2HCl —> CaCl2 + H2O + CO2
iii) Fe2O3 + 3CO —> Fe + 3CO2

Answer 14

i) Mg is oxidised as ON increases from 0 to +2, H2 is reduced as ON decreases from +1 to 0
ii) Trick question- all ON are the same so not a redox reaction
iii) Fe is reduced as the ON decreases from +3 to 0, C is oxidised as the ON increases from +2 to +4