Use of Oxidation Numbers in Nomenclature

Question 1

what is the systematic name of a compound

Answer 1

• when an element in it can have more than one oxidation state
• so roman numerals in brackets are used to clarify what the oxidation number of that element in the compound is

Question 2

what is the relative oxidation number (of the metal) and name of FeCl2 and why

Answer 2

• +2
• iron(II) chloride
• because the Fe is bonded to two chlorine atoms which would always have a o.n. of -1
• as there are two, making a total of -2, the Fe must be +2

Question 3

what is the relative oxidation number (of the metal) and name of FeCl3

Answer 3

• +3

- iron(III) chloride

Question 4

what is the relative oxidation number (of Mn) and name of KMnO4 and why

Answer 4

• +7
• potassium manganate(VII)
• the o.n. of K is +1 while for O its -2
• there are 4 O’s so the total -ve o.n. is -8
• -8 + 1 from the K = -7 that needs to be neutralised
• giving Mn +7

Question 5

what is the relative oxidation number (of Mn) and name of K2MnO4

Answer 5

• +6

- potassium manganate(VI)

Question 6

what is the relative oxidation number (of the metal) and name of CrO4(2-) and why

Answer 6

• +6
• chromate(VI) ion
• there are 4 O’s giving a total -ve o.n. of 8-
• but overall the compound has a charge of 2-
• meaning the Cr has an opposite charge 2 units below the total -ve of 8
• so Cr has an o.n. of +6 as +6 - 8 = -2

Question 7

what is the relative oxidation number (of the metal) and name of Cr2O7(2-)

Answer 7

• +6

- dichromate(VI) ion

Question 8

what is the systematic name of sulfur dioxide

Answer 8

• sulfur dioxide = SO2
• O2 = -4, so S = +4
• so its sulfur(IV) oxide

Question 9

what is the systematic name of sulfur trioxide

Answer 9

• sulfur troxide = SO3
• O3 = -6, so S = +6
• making it sulfur(VI) oxide