Oxidation and reduction

Question 1

What is the definition of oxidation.

Answer 1

Oxidation – the loss of electrons.

Question 2

What is the definition of reduction.

Answer 2

Reduction – the gain of electrons.

Question 3

What is the definition of redox.

Answer 3

Redox – reactions in which oxidation and reduction occur simultaneously.

Question 4

What is the definition of oxidation state

Answer 4

Oxidation state – the hypothetical charge on an atom in a compound assuming that the bonding is completely ionic.

Question 5

What is the oxidation state of elements?

Answer 5

Elements on their own have an oxidation state of zero.

Question 6

What is the oxidation state of a simple ion?

Answer 6

The oxidation state of a simple ion is the charge on the ion.

Question 7

What must the oxidation states in a compound add up to?

Answer 7

The total sum of the oxidation states of all elements in a compound must add up to zero.

Question 8

What must the oxidation states in a molecular ion add up to?

Answer 8

The total sum of the oxidation states in a molecular ion must add up to the charge on the ion.

Question 9

What is the maximum oxidation state of an element?

Answer 9

The maximum oxidation state of an element is its group number.

Question 10

What is the minimum oxidation state of an element?

Answer 10

The minimum oxidation state of an element is its group number -8.

Question 11

What is the oxidation state of oxygen?

Answer 11

Oxygen has an oxidation state of -2 except in peroxides where it is -1 and in OF2 where it is +2.

Question 12

What is the oxidation state of hydrogen?

Answer 12

Hydrogen has an oxidation state of +1 except in metal hydrides where it is -1.

Question 13

What is the oxidation state of group 1?

Answer 13

Group 1 elements have an oxidation state of +1.

Question 14

What is the oxidation state of group 2?

Answer 14

Group 2 elements have an oxidation state of +2.

Question 15

What is the oxidation state of transition metals?

Answer 15

Transition metals vary. The number in roman numerals in the name gives the oxidation state of the transition metal ion. E.g. Potassium manganate (VII) shows the manganese ion is +7.

Question 16

What do ions that end in –te contain?

Answer 16

Ions which end in –te contain d or p block elements and some oxygen atoms.

Question 17

What do ions that end in –ate with the oxidation state of the positively charged ion contain?

Answer 17

The ending –ate with an oxidation state shows the oxidation state of the positively charged ion e.g. sulfate (IV) sulphur is +4.

Question 18

What do ions that end in –ate without the oxidation state of the positively charged ion contain?

Answer 18

The ending –ate without an oxidation state shows that it is the highest oxidation state e.g. sulfate is sulphur +6.

Question 19

What is an increase in oxidation state called?

Answer 19

An increase in oxidation state is oxidation.

Question 20

What is an decrease in oxidation state called?

Answer 20

A decrease in oxidation state is reduction.

Question 21

What is a redox reaction?

Answer 21

A redox reaction is one in which oxidation and reduction occur.

Question 22

What is an oxidising agent?

Answer 22

An oxidising agent causes oxidation in other species and is reduced itself.

Question 23

What is a reducing agent?

Answer 23

A reducing agent causes reduction in other species and is oxidised itself.

Question 24

What do half equations show?

Answer 24

Half equations include electrons and help show the oxidation and reduction processes in a chemical reaction.

Question 25

When oxygen is added or removed in a half equation how do you balance it?

Answer 25

If oxygen atoms are added or removed from a compound or ion H2O and hydrogen ions H+ are used to balance this change in oxygen content.  

Question 26

What must happen to the charges in a half equation on the right and the left?

Answer 26

For all half equations the total charges on the left hand side and right hand side should be the same.  

Question 27

What is the first thing you need to do when combining half equations?

Answer 27

To combine the half equations you first need to make sure that there are the same number of electrons on both sides.  

Question 28

What must happen to the electrons when you combine half equations?

Answer 28

When you combine them the electrons should cancel out.  

Question 29

What happens to water or hydrogen ions if they are on both sides?

Answer 29

If H2O or H+ appear on both sides they can often be cancelled down. 

Question 30

What do you get when you combine half equations?

Answer 30

Combined half equations give an ionic equation.   

Question 31

How are organic chemicals such as primary and secondary alcohols oxidised?

Answer 31

Organic chemicals such as primary and secondary alcohols are oxidised by acidified potassium dichromate (VI) solution.

Question 32

What happens to primary alcohols when they are oxidised?

Answer 32

Primary alcohols are oxidised to aldehydes which may be further oxidised to carboxylic acids.

Question 33

What happens to secondary alcohols when they are oxidised?

Answer 33

Secondary alcohols may be oxidised to ketones. 

Question 34

How can aldehydes, ketones and carboxylic acids be reduced?

Answer 34

Aldehydes, ketones and carboxylic acid can be reduced using Lithal (LiAlH4).

Question 35

How do you represent oxidising agents in chemical reactions for organic chemicals?

Answer 35

Equations for the oxidation of organic chemicals may be written using [O] to represent the oxidising agents.  

Question 36

How do you represent reducing agents in chemical reactions for organic chemicals?

Answer 36

Equations for the reduction of organic chemicals may be written using [H] to represent the reducing agent.