How do I work out the chemical(symbol) formula for Iron(III) Sulfate(VI)?

Can someone explain the steps to work out what the chemical formula for Iron(III) Sulfate(VI) would be?

find the lowest common multiple of 3 and 4 which is 12. 3 goes into 12 4 times so it's Fe4 and 4 goes into 12 3 times so it's (SO2)3. combining that Fe4(SO2)3

(edited 7 months ago)

Reply 2

TypicalNerd

Original post by Spelunker

find the lowest common multiple of 3 and 4 which is 12. 3 goes into 12 4 times so it's Fe4 and 4 goes into 12 3 times so it's (SO2)3. combining that Fe4(SO2)3

Unfortunately, this is not the correct approach.

Iron(III) is Fe^3+
Sulphate(VI) is SO4^2-

Because you need the charges to cancel out, you ”swap” the magnitudes of the charges (i.e you ignore the + or - sign in front) to work out the ratio of anion to the cation.

Reply 3

bl0bf1sh

Original post by Blackrose06

Can someone explain the steps to work out what the chemical formula for Iron(III) Sulfate(VI) would be?

Original post by TypicalNerd

Sulphate(VI) is SO4^2-

Yeah I'd just like to add (for clarity) that the VI refers to the oxidation state of the sulphur, rather than the overall charge of the ion.
So the sulphur is +6, each oxygen is -2 (this is the case in most situations, although there are a couple of exceptions!) and there are 4 oxygens. 4 x -2 = -8 for all the oxygens. -8 + 6 = -2, which is the overall charge of the sulphate(VI) ion. :smile:

Then the general approach as described by @Spelunker would work, remembering to change the numbers so that they work with the charges of these particular ions involved (+3 and -2), ignoring the +/- signs as @TypicalNerd said :smile:

Reply 4

Scanjo63

https://www.science-revision.co.uk/finding%20the%20formula.html