redox

Question 1

oxidation

Answer 1

• gain of oxygen
• loss of electrons
• increase in oxidation number

Question 2

reduction

Answer 2

• loss of oxygen
• gain of electrons
• decrease in oxidation number

Question 3

disproportionation

Answer 3

• when a single species is simultaneously both oxidised and reduced
• use OS to work this out

Question 4

oxidising agents

Answer 4

• give oxygen to another substance
• remove electrons from another substance (so are reduced themselves)
• strongest oxidising agents are found in group 7

Question 5

reducing agents

Answer 5

• remove oxygen from another substance
• give electrons to another substance (so are oxidised themselves)
• strongest reducing agents are found in group 1

Question 6

oxidation states (OS)

Answer 6

• oxidation/reduction in covalent compounds

- instead of true loss/gain of electrons, ‘degree of sharing’ of electrons changes

Question 7

Rules for assigning OS

Answer 7

• OS of an atom in its elemental state = 0
• sum of the OS of all the atoms in a compound = 0
• OS of an ion = the charge on the ion (Cl- = -1)
• OS of a group ion = the charge on the ion
• OS of an oxygen atom in a compound = −2, except in peroxides it = -1 / when with fluorine it = +2
• OS of a hydrogen atom in a compound = +1, except in metal hydrides it = -1

Question 8

using OS to spot oxidation/reduction

Answer 8

• If the OS of an element increases, then it has been oxidised.
• If the OS of an element decreases, then it has been reduced.

Question 9

water OS

Answer 9

• oxygen = -2

- hydrogen = +1