Oxidation, Reduction And Redox

Question 1

What happens when an element is oxidised?

Answer 1

loses electrons

Question 2

What happens when an element is reduced?

Answer 2

gains electrons

Question 3

What is an oxidising agent?

Answer 3

species which gains electrons/ is an electron acceptor

Question 4

What is a reducing agent?

Answer 4

species which loses electrons/ is an electron donator

Question 5

What does an oxidation state show in an ionic compound?

Answer 5

how many electrons are gained or lost

Question 6

What does an oxidation state show in a molecule?

Answer 6

distribution of electrons between elements of different electronegativity

Question 7

What are the main principles of oxidation states?

Answer 7

-elements in uncombined state are 0
-positive, element lost electrons, oxidised
-negative, element gained electrons, reduced
-sum of all oxidation states in compound is 0 as electrically neutral
-sum of all oxidation states in complex ion is the charge of the ion

Question 8

What is the oxidation state of hydrogen?

Answer 8

+1 except in metal hydrides where it is -1

Question 9

What is the oxidation state of group one elements?

Answer 9

Always +1

Question 10

What is the oxidation state of group two elements?

Answer 10

Always +2

Question 11

What is the oxidation state of aluminium?

Answer 11

Always +3

Question 12

What is the oxidation state of oxygen?

Answer 12

-2 except in peroxides where it is -1 and in OF2 where it is +2

Question 13

What is the oxidation state of fluorine?

Answer 13

Always -1

Question 14

What is the oxidation state of chlorine?

Answer 14

-1 except in F and O where it is positive

Question 15

How do we work out oxidation states?

Answer 15

1. Start with correct formula
2. Fill in elements you know oxidation states for
3. Deduce other oxidation states
   *remember in a compound oxidation states add to 0 and in a complex ion they add to the charge of the ion

Question 16

What happens to the oxidation state of a reduced element?

Answer 16

decreases

Question 17

What happens to the oxidation state of an oxidised element?

Answer 17

increases

Question 18

How can we balance redox equations using both our understanding of reduction, oxidation and oxidation states?

Answer 18

1. Write oxidation state above each species
2. Identify species reduced and species oxidised
3. Write half equations for species reduced and species oxidised
4. Balance number of electrons transferred for each half equation
5. Include information in unbalanced redox equation
6. Balance remaining atoms that haven’t been oxidised or reduced

Question 19

If a species is reduced where are the electrons gained?

Answer 19

Left hand side of equation

Question 20

If a species is oxidised where are the electrons lost?

Answer 20

Right hand side of the equation

Question 21

What is a disproportionation reaction?

Answer 21

atom of the same element has been both reduced and oxidised