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How to derive this equation? (Potassium Dichromate and iron)

In a titration, 0.321 g of a moss killer reacted with 23.60 cm3 of acidified
0.0218 mol dm–3 K2Cr2O7 solution.
Calculate the percentage by mass of iron in the moss killer. Assume that all of the iron
in the moss killer is in the form of iron(II).

I understand the steps i need to take to solve this question. However, for one step, you need to use the ration between moles of dichromate ions and iron ions - which means you need the equation:

Cr2O72– + 14H+ + 6Fe2+ 2Cr3+ + 7H2O + 6Fe3+

Basically, how am i supposed to derive this equation?

Any help would be appriciated.

Reply 1

EierVonSatan

You should just memorise the dichromate half equation, it comes up a lot :yes:

same with the permanganate version. To do it from sratch you still need to remember the oxidation states of chromium before and after.

Then you can just tailor it to what ever you need oxidising, in this case iron :smile:

Reply 2

Catalyst

Thanks, i was wondering if memory might be involved :P

It makes sense now, i had a similar question where you had to combine the dichromate half equation with iron before xD