chem crswrk plan

for the plan i have to do a back titration to determine the concentration of chlorine, i get kinds wot i ave 2 do, but the beginining bit is confusing me.

1- react chlorine with reducing agent such as an iron 2 compound.

firstly, what compound? is FeSO4 ok? and then how do you write the equation.

FeSO4 + Cl2 --> FeCl2 + ..... ?

i think this should be easy, but i cant think.... i know the SO4 is a spectator ion, but where does it go?

plz help ppl! :smile:

Reply 1

verityreeves

plz help sum1!

i'll type exactly what i have to do...

To determine the concentration of a saturated solution of chlorine.
In the first stage of the proceduce, the solution of chlorine is added to an excess of a suitable reducing agent such as an iron(ll) compound.

I'm stuck on the equation for this reaction.

Reply 2

charco

Study Forum Helper

the iron is oxiised from iron II to iron III in the presence of dilute H2SO4

Fe2+ --> Fe3+ + 1e
Cl2 + 2e --> 2Cl-

doubling the first and adding
2Fe2+ + Cl2 --> 2Fe3+ + 2Cl-

is the ionic equation for the first reduction. If you want to add in the spectator ions (eg SO42-) you get:

6FeSO4 + 3Cl2 --> 2Fe2(SO4)3 + 2FeCl3

but there is never any need to include the spectator ions as the MUST be correct if you have balanced the redox half equations correctly for ions and charges.

OK so once you have reduced all of the chlorine with excess Fe2+ you simply titrate this excess against a suitable oxidising agent...

thank you muchly!

hi people I'm just doing my plan I'm putting the KMnO4 in the burrette, and the H2SO4 in the solution created in part one? Is that totally worng? what wil the oclour change be? thanks muchos!xx

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