Topic 3: Redox I

Question 1

what is meant by the term ‘oxidation number’?

Answer 1

oxidation number is the charge that an ion has or the charge that it would have if the species were fully ionic

Question 2

Explain oxidation

Answer 2

oxidation is loss of electrons, loss of hydrogen or gain of oxygen

Question 3

Explain reduction

Answer 3

Reduction is gain of electrons, gain of hydrogen or loss of oxygen

Question 4

Explain a disproportionation reaction

Answer 4

a disproportionation reaction involves an element in a single species being simultaneously oxidised and reduced

Question 5

Why is oxidation number useful?

Answer 5

oxidation number is useful to classify reactions as redox and as disproportionation

Question 6

What is the general rule with metals and non-metals and oxidation number?

Answer 6

metals, in general, form positive ions by loss of electrons with an increase in oxidation number
non-metals, in general, form negative ions by gain of electrons with a decrease in oxidation number

Question 7

How do you write ionic half-equations and use them to construct full ionic equations?

Answer 7

1) write out the equation
2) check the ATOMS balance
3) write oxidation numbers
4) Add in the required number of electrons
5) add H+ ONLY if the charges are not balanced
6) add H20 if you need to balance ATOMS

Question 8

What are oxidising agents?

Answer 8

They oxidise the other species by removing its electrons. The oxidising agent is reduced in the process

Question 8

What are reducing agents?

Answer 8

A reducing agent reduces the other species by adding electrons to it. It is oxidised in the process

Question 9

What is the oxidation number of an element uncombined with other elements?

Answer 9

Oxidation number of an element uncombined with other elements is always 0, even if they’re diatomic molecules like 02

Question 10

What’s the sum of the oxidation numbers equal to?

Answer 10

It is equal to the total charge of the species eg 0 if it’s a neutral compound or +1 if it’s a positive ion

Question 11

What is the oxidation state of H?

Answer 11

H is always +1 BUT if it’s bonded to a metal it has a -1 oxidation state

Question 12

What is the oxidation state of oxygen?

Answer 12

Always -2 BUT if it’s a peroxide such as Na2O2 or H2O2 it has -1 oxidation state

Question 13

What’s the oxidation state of Fluorine?

Answer 13

-1

Question 14

What is the rule with ions and their oxidation numbers?

Answer 14

Ions always have oxidation numbers equal to their charge

Question 15

What’s the oxidation number of iron in iron (III) chloride?

Answer 15

+3