Oxidation and reduction

Question 1

What’s oxidation

Answer 1

Oxidation = oxygen added, electrons lost

Question 2

What’s reduction

Answer 2

Reduction+ Oxygen is removed, electrons gained

Question 3

What do reducing agents do?

Answer 3

Give away electrons

Question 4

What do Oxidising agents do?

Answer 4

Accept electrons

Question 5

What do oxidation states tell us in ionic compounds?

Answer 5

How many electrons in compound have been lost or gained

Question 6

True or false? Every element in its uncombined state has an oxidation state of zero?

Answer 6

True

Question 7

What do positive and negative numbers mean?

Answer 7

\+ = oxidised as element has lost electrons
- = reduced as element has gained electrons

Question 8

What is the positive and negative number correlation?

Answer 8

more + number = more oxidised

more - number = more reduced

Question 9

True or false? Numbers always have + or - sign unless they’re zero.

Answer 9

True

Question 10

What are the rules for finding oxidation states?

Answer 10

1. Uncombined elements have oxidation state of 0
2. Some elements in all of their compounds have same oxidation states
3. Sum of all oxidation states in a compound = 0
4. Sum of all oxidation states of a complex ion = charge of ion
5. In compounds the most electronegative element always has a negative oxidation state.

Question 11

Monatomic elements?

Answer 11

Oxidation state is same as their charge

Question 12

Hydrogen - oxidation state, E.g

Answer 12

+1 (except metal hydrides), HCl

Question 13

Group 1 - oxidation state, E.g

Answer 13

+1, NaCl

Question 14

Group 2 - oxidation state, E.g

Answer 14

+2, CaCl2

Question 15

Aluminium - oxidation state, E.g

Answer 15

+3, AlCl3

Question 16

Oxygen - oxidation state, E.g

Answer 16

-2, (-1 in peroxides/ =2 in components with OF2), Na2O

Question 17

Flourine - oxidation state, E.g

Answer 17

-1, NaF

Question 18

Chlorine - oxidation state, E.g

Answer 18

-1, (+ in compounds with F and O), NaCl

Question 19

Process of working out a compounds oxidation states?

Answer 19

Need a periodic table to use.

• Find oxidation states of elements in compound using periodic table
• Apply oxidation state rules to a compound
• Add up pluses and minuses to find compounds oxidation state.

Question 20

Example of finding oxidation state?

Answer 20

Ammonia (NH3)

• Hydrogen oxidation state is +1
• Nitrogen must therefore be -3 as three hydrogens makes +3 and ou need to equal zero.
• Rule 5 - Nitrogen is more electronegative than hydrogen, so hydrogen must have a positive oxidation state.

Question 21

Known Oxidation states through periodic table are?

Answer 21

Group 1 = +1
Group 2 = +2
Group starting with Boron = +3
Group starting with carbon = +/- 4
Group starting with Nitrogen = -3
Group starting with oxygen = -2
Group starting with florune = -1
Noble gases = 0