Oxidation and Reduction

Question 1

What is oxidation?

Answer 1

• Element has lost electrons- Oxidation number increases

Question 2

What is reduction?

Answer 2

• Element has gained electrons- Oxidation number decreases

Question 3

What is the rule for the oxidation states of elements?

Answer 3

The oxidation state of an uncombined element is 0 and elemental ions have oxidation states equal to their charge

Question 4

What is the rule for the oxidation states of compounds?

Answer 4

Overall oxidation state of a compound is 0 unless it is a molecular ion, in which case the oxidation state is equal to the charge

Question 5

What are the oxidation state rules?

Answer 5

• H = +1 (except for metal hydrides) - O = -2 (except for peroxides)- Group 7 = -1 (except for when combined with a more electronegative element)- Group 1 = +1- Group 2 = +2- Aluminium = +3

Question 6

How can REDOX equations be used to identify what is the oxidising agent and what is the reducing agent?

Answer 6

1 - Label oxidation states2 - Spot the changes3 - Identify what is being oxidised and reduced and by how much 4 - If oxidised then reducing agent, is reduced then oxidising agent

Question 7

What is disproportionation?

Answer 7

When an element is simultaneously oxidised and reduced

Question 8

What do half equations show?

Answer 8

The loss or gain of electrons of each species in an equation

Question 9

How can half equations be written?

Answer 9

1 - Determine oxidation states 2 - Spot changes in redox 3 - 1 electron lost = +1 change in oxidation state 1 electron gained = -1 change in oxidation state 4 - Construct half equations

Question 10

How can you construct a complete redox equation from 2 half equations?

Answer 10

1 - Balance the electrons in the 2 half equations2 - Cancel electrons3 - Combine equations 4 - Look for further cancelling

Question 11

What is sometimes needed for REDOX reactions to occur?

Answer 11

H+ ions

Question 12

How can you work out the amount of H+ needed in a REDOX reaction is acidic conditions?

Answer 12

1 - Balance the REDOX species2 - Balance the O in the reactants with water in the products3 - Add H+ ions to the reactants to balance out then water

Question 13

How can you write an ionic equation?

Answer 13

1 - Write the full equation with state symbols2 - ‘Split’ any soluble compounds 3 - Remove spectator ions