#1
What is the equation for

KMnO4 + Fe(2+ superscript) -->


and can you explain why? I havent done chemistry in 2.5 years and I cant remember shit.
#2
Cause we all have crappy memorys,like i can still remember when i was 6 an got this toy for my birthday that shot a little plastic missle,and i lost it my first day.
#3
haha "superscript". 'Tis no regular script. Yarrrr. 'Tis super. Yaaarrrrr. haha. pirates...
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im to tired and confused to comprehend what you said.
#5
Are you heating it, adding it to a solution, or what? It depends on what you plan on doing with those substances.
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#6
Its a titration. I probably should have said that.

They are both aequeus or however the **** you spell it.
#7
Potassium permanganate produces a lot of oxygen when heated so I think this would form FeO with the iron ions. Can't remember what the permanganate would reduce to though. Ain't done chemistry in ... 7 months.

Edit: It's a titration? Now you tell us ...

The only help that I can provide now is that the word is "aqueous".
Last edited by Malakian88 at Jan 15, 2007,
#8
This is an electrochemical cell question.

Ok basically, write your two half equations, with the more positive charged species on the Left Hand Side.

MnO4- +8H+ ===> Mn2+ + 4H2O
5Fe3+ +5e-<=== 5Fe2+

Find the standard electrode potential for each of these cells using a data book.

Write the half cell with the most negative ECell on top.

Which would go as such (I think these are the ECells, I may be wrong)

5Fe3+ +5e-<=== 5Fe2+ Ecell = +0.77
MnO4- +8H+ ===> Mn2+ + 4H2O Ecell = +1.50 or + 1.51

Now the anticlockwise rule is that LORA - Left Oxidises Right Above. The manganate oxidises the Iron to it's 3+ oxidation number.

Calculate the overall Ecell - its 1.51 - 0.77 = +0.74 V

You have a large Total E cell for this reaction therefore it is likely that this reaction will go to completion.

Combine these two half cells to provide the final equation.

MnO4- +8H+ + 5Fe2+===> Mn2+ + 4H2O + 5Fe3+

Remember that this does not tell us anyhthing about the rate at which this reaction will go.

Hemant

EDIT:

As for why, this is a standard redox reaction. The Iron is being oxidised and the manganate ion is being reduced. This is because the iron is a good giver of electrons. The manganate will accept electrons, and is reduced. If one thing is reduced, the other must be reduced to provide the electrons for the reduction.

I don't know what level you're at so I've kept it basic.
Last edited by hemantmaan at Jan 15, 2007,
#9
Where did the H+ come from? I really dont think its an electrochemical cell problem, because we have never done that and there are no questions on voltage.

The question is "Write the equation for the reaction of permanganate ions with iron(II) ions and use it to calculate the number of moles of Fe2+(aq) present in the 25.00ml sample.
#10
Just curious, if you haven't done chem in 2.5 years, what is this for?
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#11
Quote by huk
Where did the H+ come from? I really dont think its an electrochemical cell problem, because we have never done that and there are no questions on voltage.

The question is "Write the equation for the reaction of permanganate ions with iron(II) ions and use it to calculate the number of moles of Fe2+(aq) present in the 25.00ml sample.


Well either way you write out the half cells and combine them.

Though to know which one is happening (Fe2+ ==> Fe3+ or Fe(s)) Ecells can help, as they will tell you how feasible a reaction is.

Either way, it is the equation at the bottom.

To work out the moles, you need to know a concentration of something.

This is because the volume is related to mols via concentration.

The units of concentration is moldm^-3, which is your mols divided by your concentration. If you're trying to work out the mols, you need the concentration.
Last edited by hemantmaan at Jan 15, 2007,
#12
the concentration of kmno4 is 0.01988 mol/L

used 25.41 ml of it.
#13
Quote by E Daws
Just curious, if you haven't done chem in 2.5 years, what is this for?



I changed my degree recently, and it requires another chem course.
#14
Right now look:

conc of MnO4- = 0.001988

you used 25.41 ml / cm3 of it.

Mols = conc x vol/1000 (because its in cm3)

= 0.001988 x 25.41 /1000

= 0.00005051508 mols

You used 5 mols of Fe2+ for every mol of MnO4- so multiply this by 5

0.0000505... * 5 = 0.000253 mols of Fe2+


EDIT: the H+ ions come from the acidic conditions you would supply for this reaction.
Last edited by hemantmaan at Jan 15, 2007,
#16
Sorry for all the stupid questions, but where did the K go?


Wait nevermind, it didnt ask for potassium
#17
What degree are you doing?

ml and cm^3 are the same.

1 litre is 1 dm^3

1dm^3 = 1000ml = 1 Litre

1dm^3 = 1000cm^3

Therefore 25ml = 25cm^3

The potassium is a spectator ion and hence doesn't take part in the reaction. Therefore we omit it from the half cells and indeed, the ionic equation.