Oxidation, Reduction and Redox

Question 1

Redox

Answer 1

A reaction where one substance loses electrons and is oxidised, while another substance gains electrons and is reduced

Question 1

Oxidation number

Answer 1

Number assigned to an atom in a substance and represents the number of electrons lost or gained by an atom of an element

Question 2

What is the oxidation number of an element

Answer 2

0

Question 3

What happens to the oxidation number during oxidation

Answer 3

Oxidation number increases

Question 4

What happens to the oxidation number during reduction

Answer 4

Oxidation number goes down

Question 5

Oxidising agent

Answer 5

A substance that oxidises another substance by removing electrons from it. (It is also the substance which is reduced)

Question 6

Reducing agent

Answer 6

A substance that reduces another substance by donating electrons to it. ( it is also the substance which is oxidised)

Question 7

Half equation for the reduction of H+ ions

Answer 7

2H20 + 2e ——–> 2OH- + H2

Question 8

How to do half equations for oxidation

Answer 8

x ——-> y + e

Question 9

How to do half equations for reduction

Answer 9

x + e- ——–> y

Question 10

How do you combine half equations to form the overall reactions

Answer 10

1. Find out which equation is reduction and which is **oxidation **
2. Re-write the equations, balancing them and adding the e- accordingly to balance the charges
3. Get the same number of electrons in both equations by multiplying one or both of the equations
4. Cancel out the extra ions/substances.
5. Things on the left can only cancel out with things on the right

Question 11

Half equation for the reduction of MnO4

Answer 11

MnO4- + 8H+ 5e- ———> Mn2+ + 4H20

Question 12

What is the colour of MnO4 / manganate ion

Answer 12

Purple

Question 13

What is the half equation for the reduction of Cr2O7

Answer 13

Cr2O7 2- + 14H+ + 6e- ——–> Cr 3+ + 7H2O

Question 14

Colour of Cr2O7 2- ion

Answer 14

Orange

Question 15

Colour of Cr 3+ ion

Answer 15

Green

Question 16

Half equation for oxidation of S2O3 2-

Answer 16

2S2O3 2- ——-> S4O6 2- + 2e-

Question 17

Disproportionation reaction

Answer 17

A reaction in which an element is both oxidised and reduced in the same reaction

Question 18

How do you know if one ion/element is a better oxidising or reducing agent

Answer 18

The higher the increase/decrease in oxidation number, the better/stronger it is.

If change in oxidation number is the same, compare the electronegativities.
Better oxidising agent = Higher electronegativity
Better reducing agent = Lower electronegativity