Redox

Question 1

In terms of oxygen define oxidation

Answer 1

Gaining oxygen

Question 2

In terms of oxygen define reduction

Answer 2

Loss of oxygen

Question 3

In terms of oxygen define an oxidising agent

Answer 3

Provides oxygen and is in itself reduced

Question 4

In terms of oxygen define a reducing agent

Answer 4

Removes oxygen and is in itself oxidised

Question 5

In terms of hydrogen define oxidation

Answer 5

Loss of hydrogen

Question 6

In terms of hydrogen define reduction

Answer 6

Gain of hydrogen

Question 7

In terms of hydrogen define an oxidising agent

Answer 7

Removes hydrogen and is in itself reduced

Question 8

In terms of hydrogen define a reducing agent

Answer 8

Gains hydrogen and is in itself oxidised

Question 9

In terms of electrons define oxidation

Answer 9

Loss of electrons

Question 10

In terms of electrons define reduction

Answer 10

Gain of electrons

Question 11

In terms of electrons define an oxidising agent

Answer 11

Gains electrons and is in itself reduced

Question 12

In terms of electrons define a reducing agent

Answer 12

Loss of electrons and is in itself oxidised

Question 13

What is the oxidation number of an uncombined element or one combined with itself?

Answer 13

Always zero

Question 14

What is the oxidation number of a simple ion (with only 1 element)?

Answer 14

Equal to its charge

Question 15

What is the oxidation number of all group 1 elements?

Answer 15

Always +1

Question 16

What is the oxidation number of all group 2 elements?

Answer 16

Always +2

Question 17

What is the oxidation number of hydrogen?

Answer 17

+1, except in metal hydrides of group 1 and 2 wher e it becomes -1

Question 18

What is the oxidation number of oxygen?

Answer 18

-2, except in peroxides (e.g. H2O2) where it becomes -1, and oxygen fluoride where it becomes +2

Question 19

What is the oxidation number of fluorine?

Answer 19

Always -1

Question 20

What is the oxidation number of chlorine?

Answer 20

Usually -1 (like in metal chlorides), but it changes when other non-metals are present

Question 21

What is the oxidation number of a compound ion?

Answer 21

The sum of the oxidation numbers is equal to the charge on the ion

Question 22

What is the definition of oxidation number?

Answer 22

The charge that a species would have if it was a simple ion

Question 23

What is a disproportionation reaction?

Answer 23

The simultaneous oxidation and reduction of an element in a single species

Question 24

Points for writing half equations

Answer 24

• reactions on the left and products on the right
• state symbols are usually included
• for an oxidation reaction, electrons can be shown on the left or the right
• for a reduction reaction, electrons are shown on the left
• the reaction must balance for charge

Question 25

Writing a half equation for reduction (under acidic conditions)

Answer 25

After putting in the correct number of electrons gained, add H+ on the left and water on the right, then balance

Question 26

Writing a half equation for oxidation (under alkaline conditions)

Answer 26

After putting in the correct number of electrons lost, add OH- on the left hand side and H2O on the right, then balance the charge by adding extra OH- ions

Question 27

Combining half equations using the ion-electron method

Answer 27

Multiply one or both of the half equations so that the number of electrons lost or gained becomes the same in both equations, then add the two together to get the overall equation

Question 28

Combining half equations using the oxidation number method

Answer 28

number of atoms of A x change in oxidation number of A = number of atoms of B x change in oxidation number of B