2.1.4 Redox

Question 1

what are oxidation numbers

Answer 1

They are a means of keeping track of electron loss and gain during reactions.
Each element is assigned an oxidation number, if this changes during the reaction then a redox process has taken place.

Question 2

List the rules of assigning oxidation numbers

in order

Answer 2

1. All elements in their natural state: oxidation no. = 0
   The total of the oxidation no. of a compound = 0.
   The total of the oxidation no. of ions = the change on the ion.
2. In a compound or ion the oxidation no. of elements in groups 1,2,3 are +1,+2,+3 respectively.
3. In a compound or ion the oxidation no. of fluorine = -1
4. In a compound or ion the oxidation no. of hydrogen is +1
5. In a compound or ion the oxidation no. of oxygen = -2
6. In a compound or ion the oxidation no. of chlorine = -1
7. The oxidation states of other elements are determinded by ensuring that the compound or ion obeys rule 1.

Question 3

what are the special cases of oxidation numbers

Answer 3

Hydrogen in metal hydrides = -1 (eg. NaOH, CaH2)
Oxygen in peroxides = -1 (eg. H2O2)
Oxygen bonded to Fluorine = +2 (eg. F2O)

Question 4

why are roman numerals used with oxidation numbers

Answer 4

Roman numerals are used in the names of compounds that form ions with different charges. The numeral shows the oxidation number of the element without a sign. The sign of the oxidation state is obvious from the overall charge. eg. Iron (II) = Fe2+ and Iron (III) = Fe3+

Question 5

when are roman numerals ommited

Answer 5

with the most common ion eg. when nitrate is NO3- or when sulfate is SO42-

Question 6

roman numerals without the sign examples

Nitrate

Answer 6

NO2- = Nitrite = +3 oxidation number -> becomes nitrate (III)
NO3- = nitrate = +5 oxidation number -> become nitrate (v) but the numeral will often be omited due to it being the most common ion.

the change is due to it using a systematic name instead

Question 7

explain redox process

Answer 7

A redox process involves the transfer of electrons from one substance to another.

eg. combustion, rusting and the reaction of acids with metals

Question 8

What does OIL RIG represent

Answer 8

Oxidation Is Loss
Reduction Is Gain

OF ELECTRONS

and hydrogen

Question 9

How is the oxidation number effected by reduction

Answer 9

Reduction causes the oxidation number to decrease

Question 10

How is the oxidation number affected by oxidation

Answer 10

Oxidation causes the oxidation number to increase

Question 11

what is a redox reaction which involves the same element being both oxidised and reduced called

Answer 11

disproportionation reaction

Question 12

define disproportionation reaction

Answer 12

A redox reaction in which the same element is both oxidised and reduced.