Redox reactions

Question 1

what is a redox reaction

Answer 1

a reaction where the oxidation states of atoms are changed

Question 2

define reduction

Answer 2

• gain of electrons (most important definition for alevel chem)
• addition of hydrogen
• removal of oxygen

Question 3

define oxidation

Answer 3

• loss of electrons
• removal of hydrogen
• addition of oxygen

Question 4

What is meany by ‘oxidation number’

Answer 4

Charge that a species would have if it were fully ionic

Question 5

what is a reducing agent and what does it do

Answer 5

Species that donate electrons to another species (so it becomes reduced). The reducing agent itself becomes oxidised as it has loss electrons.

Question 6

state the oxidation number rules; (7 in total)

Answer 6

• oxidation number of an uncombined element is 0
• sum of oxidation number of all elements in a neutral compound is 0
• sum of oxidation numbers of elements in an ion is equal to the overall charge of the ion
• The more electronegative element in compound is given the negative oxidation number
• Oxidation number of fluorine is always -1
• Oxidation number of hydrogen is +1 except when combined with a less electronegative element then it becomes -1
• Oxidation number of oxyen is -2 except when in peroxides where it becomes -1 and when combined with fluorine where it becomes positive

Question 7

what is meant by a disproportionation reaction

Answer 7

When a species has been both reduced and oxidised in the same reaction

Question 8

what does an increase in oxidation number tell us has happened to the atom?

Answer 8

An electron has been lost

Question 9

what does a decrease in oxidation number tell us has happened to the atom?

Answer 9

An electron has been gained

Question 10

How do you figure out if something has been oxidised or reduced

Answer 10

Write down oxidation number before and after reaction, then from figures, decide