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sarah1004 · Nov 17, 2009, 11:27 PM

write the balanced chemical equation for the reaction of Fe2+ with MnO4- in acidic solution.

I did it , but I am not sure. Please check it for me

H^+ + MnO4^- + Fe2+ ---------------> Mn2+ + Fe3+ + H2O

pramod awasthi · Nov 18, 2009, 05:31 AM

Ok I am trying
I think it can solve by ion electron method so note that steps
divide reaction in half reduction and half oxidation reaction

MnO4^- + H^+ +Fe^2+ ============> Mn^+2 +Fe^+3 +H2O
and note balance reacton dear its long method sorry ;)
MnO4^- +8H^+ +5Fe^+2==========>Mn^+2 +5Fe^+3 + 4H2O

I think u can understand my problem dear it is right
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Pramod awasthi

Unknown008 · Nov 18, 2009, 06:08 AM

I'll show you the way I do it:

Write the first ionic equation occuring: oxidation of Fe (II) to Fe (III)

$Fe^{2+} \rightarrow Fe^{3+} + e^-$

Now the second equation occurring: reduction of MnO4^- to Mn^2+

$MnO_4\ ^- + 8H^+ +5e^- \rightarrow Mn^{2+} + 4H_2O$ (that you have to balance)

Now, ensure that there is an equal amount of electrons in both equations. For that, multiply each term in the first equation by 5:

$5Fe^{2+} \rightarrow 5Fe^{3+} + 5e^-$

Now add both, crossing out the terms appearing on both sides of the equation:

$MnO_4\ ^- + 8H^+ +\cancel{5e^-} + 5Fe^{2+} \rightarrow Mn^{2+} + 4H_2O + 5Fe^{3+} + \cancel{5e^-}$

$MnO_4\ ^- + 8H^+ + 5Fe^{2+} \rightarrow Mn^{2+} + 4H_2O + 5Fe^{3+}$

Lastly, check if all is right. Yes, it is :)

sarah1004 · Nov 18, 2009, 05:58 PM

Thanks~~
how about this one?
Fe^2+ + Cr2O7^2- -------------> Fe^3+ + Cr^3+
I did it...
6Fe^2+ + Cr2O7^2- + 14H^+ -------------> 6Fe^3+ + 2Cr^3+ + 7H2O
I hope it is corret..

when a 0.8g sample of an unknown Fe^2+ salt is titrated with 0.0285M K2Cr2O7, it is found that 59.2mL of this dichromate solution are required to reach the endpoint. Calculate the percent iron in the unknown using the balanced equation in 6Fe^2+ + Cr2O7^2- + 14H^+ -------------> 6Fe^3+ + 2Cr^3+ + 7H2O.

how can I find percent iron ?

please help me Thanks

Unknown008 · Nov 19, 2009, 08:34 AM

Yes, it is correct :)

1. Find the number of moles of potassium dichromate reacting, using concentration and volume.
2. Use your equation to deduce the number of moles of iron (II) that reacted.
3. Find the mass of that amount of iron (II)
4. Divide the mass of iron (II) by the mass of iron sample, multiplied by 100% to get the percentage iron. (It's the fraction of iron (II) in that sample, converted to percentage)

Pramod, I use the LaTeX facility of the forum, click on the quote button and you'll see that I used the 'math' tabs, together with some functional codes.