[zimrock]

potassium oxalate is titrated against KMnO4 solution to give ferric ion , carbon dioxide and Mn2+ ion. 100 ml of .1M KMnO4 solution is used. The resulting carbon dioxide is treated with V ml of NaOH (.1M) solution. what is V?

according to the answer, the number of equvalents of potassium permanganate is not equal to number of equvalents of carbon dioxide liberated. how?

[Borek]

potassium oxalate is titrated against KMnO4 solution to give ferric ion

Huh?

Write all balanced reaction equations.

[zimrock]

FeC2O4  +  KMnO4 +  H+  ---> Fe3+  + CO2   + Mn2+.

solve the problem

[zimrock]

and,,
CO2 + NaOH ---> Na2CO3

[Borek]

So it is ferric oxalate, not potassium.

Start balancing reactions.

[zimrock]

oops. sorry about that typo.

why is it necessary to balance the reactions?

isnt it right to say, the equvalents of KMnO4= eq of CO2 = eq of NaOH ?

[Borek]

why is it necessary to balance the reactions?

isnt it right to say, the equvalents of KMnO4= eq of CO2 = eq of NaOH ?

You have to know what equivalents are and thet's defined by the reaction equation. And balanced one. Depending on the reaction 1 mole of MnO₄^- can be 1, 3 or 5 equivalents (at least).

[zimrock]

that doesnt exactly help me solving the problem.

Please post a solution

[Borek]

that doesnt exactly help me solving the problem.

As far as I can tell you have not tried yet.

Please post a solution

Please read forum rules. And please balance the reaction equations, as thats the first step to solution.

[zimrock]

5C2O4 (2-) + 16H+ + MnO4-  ---> 10CO2 + 8H2O + 2 Mn2+

i dont really see why this would help

[Borek]

Almost correct, but I suppose it is just a typo (lacking 2).

Now, looking at this reaction equation - what is ratio of permanganate to oxalate? How many moles of permanganate per mole of oxalate? What is permanganate equivalent?

[zimrock]

two moles of permanganate for every 5 moles of oxalate.

one sec.
i think i've got my definition of equivalents wrong.
Isnt there 5 moles in one equavalent of permanganate and 2 moles in one equivalent of oxalate by just seeing the change in oxidation state?

[Borek]

i think i've got my definition of equivalents wrong.

That's I supposed from teh very beginning

Isnt there 5 moles in one equavalent of permanganate and 2 moles in one equivalent of oxalate by just seeing the change in oxidation state?

Quite the opposite - in this case there are 5 equivalents in 1 mole of permanganate (thus 1 equivalent is 0.2 mole). But you are right about the oxidation state part.

Problem with equivalents is that they can't be calculated once and for ever, as the substance can behave differently in different reactions. So 1 mole of permanganate is 5 equivalents for redox reactions as long as we are talking about oxidation is acidic solution.

[zimrock]

ok got that.

but what is the purpose of balancing this equation and what is the next step in solving this problem

[Borek]

Now it is simple stoichiometry - and stoichiometry always require balanced equations. You know amount of permanganate used, that plus the reaction equation is enough to calculate amount of CO₂ produced - that goes into the second reaction and gives amount of NaOH necessary for neutralization.