2.1.5 Redox

Question 1

What does oxidation state represent?

Answer 1

The degree of oxidation a particle undergoes based on the assumption that electrons are completely transferred between atoms

Question 2

What does a positive oxidation number show?

Answer 2

That the element has been oxidised

Question 3

What does a negative oxidation number show?

Answer 3

That the element has been reduced

Question 4

What is the oxidation state of an uncombined element?

Answer 4

Always 0
E.g. Cl2, Fe, O2

Question 5

What is the oxidation state of an ion?

Answer 5

Same as its charge
E.g. Ca2+ = +2

Question 6

What is the oxidation state of a group 1 element?

Answer 6

Always +1
E.g. KCl

Question 7

What is the oxidation state of a group 2 element?

Answer 7

Always +2
E.g. CaO

Question 8

What is the oxidation state of aluminium?

Answer 8

Always +3
E.g. Al2O3

Question 9

What is the oxidation state of hydrogen?

Answer 9

Usually +1 except in metal hydrides when it is -1
E.g. HF, NaH

Question 10

What is the oxidation state of chlorine?

Answer 10

Usually -1 except in compounds when F and O when it is positive
E.g. KCl, ClF3

Question 11

What is the oxidation state of fluorine?

Answer 11

Always -1
E.g. KF

Question 12

What is the oxidation state of oxygen?

Answer 12

Usually -2 except in peroxides when it is -1 and in F2O when it is +2

Question 13

What must the sum of oxidation states in a compound equal?

Answer 13

0

Question 14

What do roman numerals indicate?

Answer 14

The magnitude of the oxidation number when an element may have compounds/ions with different oxidation numbers
E.g. Iron (II) = +2, iron (III) = +3

Question 15

What is oxidation?

Answer 15

The loss of electrons

Question 16

What is reduction?

Answer 16

The gain of electrons

Question 17

What are reactions called which involve both oxidation and reduction?

Answer 17

Redox

Question 18

What are reducing agents?

Answer 18

• Lose electrons
• Oxidised themselves

Question 19

What are oxidising agents?

Answer 19

• Gain electrons
• Reduced themselves

Question 20

How are oxidation and reduction shown through oxidation numbers?

Answer 20

• An increase in oxidation number (more positive) shows oxidation
• A decrease in oxidation number (more negative) shows reduction

Question 21

What happens when metals react with acids?

Answer 21

• Oxidised
• Form hydrogen and a salt

Question 22

What is the WHE method for half equations?

Answer 22

1. Calculate oxidation states on each side of the equation
2. Balance the element changing oxidation state
3. Balance oxygen atoms by adding water molecules
4. Balance hydrogen by adding H+ ions
5. Balance the charge by adding electrons

Question 23

What does the side the electrons are on tell you?

Answer 23

• If electrons are on the left, it is reduction
• If electrons are on the right, it is oxidation

Question 24

How do you combine half equations?

Answer 24

• The number of reactants and products must balance
• The charges must balance
• If there is something on both sides of the equation (e.g. electrons, hydrogen), the equation can be simplified
• The number of electrons must be the same in both half equations for them to be combined