3.2 [Oxidising and reducing agent]

Question 1

What is the problem with oxidation and reduction for covalent compounds?

Answer 1

Oxidation and reduction for atoms and ions is relatively simple to see which element or ion gets oxidised loses electrons and which one gets reduced gains electrons this is more difficult for covalent compounds which is why the oxidation number is developed.

Question 2

What is the oxidation number?

Answer 2

Oxidation number is the charge that an ion has or the charge that it would have if the species were fully ionic.
For MgO charge of Mg = 2 charge of O = -2

Question 3

What are the rules for determining oxidation numbers?

Answer 3

Oxidation of uncombined elements is 0

The sum of the oxidation numbers of all of the elements in a neutral compound is 0

The sum of oxidation numbers of all the elements in a ion is equal to the charge of the ion

The more electronegative element in a substance is always given a negative oxidation number

The oxidation number of fluorine is always -1

The oxidation number of hydrogen is 1 except when combined with a less electronegative element then it is -1

Oxidation number of oxygen is -2 except in peroxides where it is -1 when combined with fluorine when it is positive

Question 4

How can oxidation numbers be used to classify a reaction

Answer 4

Zn > Zn 2+ + 2e-
Electrons has been lost, An element is oxidised when its oxidation number increases, More positive

Cl2 + 2e- > 2Cl-
Has gained electrons, An element is reduced when its oxidation number decreases. Less positive.

Question 5

What are systematic names?

Answer 5

When an element has more than 1 oxidation state the names of its compounds and ions contain the oxidation number of the element. written in roman numerals.

Like FeCl2 written as iron(II)Chloride
KMn04 Potassium Manganate (VII)

Question 6

Wat are disproportionation reactions?

Answer 6

Disproportionation is the simultaneous oxidation and reduction of an element in a single reaction.

Question 7

How are full equations written from ionic half equations?

Answer 7

Solid zinc added to copper (II) sulfate following changes take place

Zn > Zn2+ + 2e- and Cu2+ + 2e- > Cu
Zn + Cu2+ > Zn2+ + Cu

When acidified aqueous solution potassium manganate added to iron (II) sulfate following changes occur
Fe2+ > Fe3+ +e- and MnO4- + 8H+ +5e- > Mn2= + 4H20
Balancing

5Fe2+ > 5Fe3+ + 5e- MnO4- + 8H+ +5e- > Mn2+ + 4H20