Destroyer Normality Q 70

[Pennpaki]

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So I simply can't understand this normality question on Destroyer and why they are choosing to use the normality of electrons transferred:

Q) consider the following rxn of 2.5 M of dichromate

Cr2O^ 2- ----> Cr3+ ( acidic medium)

What is the solution normality upon completion?

The answer is 7.5 N

They compared the oxidation states of Cr from + 6 to +3 and then used this 3 e- value and multiplied it to 2.5 M to get the normality .... this is the normality of what?!

I would think we'd simply multiply 2.5 with 2( because each Cr2O7 has 2 moles of Cr...) and that would be the normality?

 

[rickblas]

I believe in this term the equivlants he is using for normality is the mols of e- which is 3 because this is a redox rxn. So basically since normality is N(equivilants)XM(molarity) it is just the equivilants of the e- (3) times 2.5 = 7.5.

anyone else care to explain better? thats my reasoning though!

 

[Pennpaki]

yea but how are we supposed to know he's asking for the e normality and not Cr? Can anyone elaborate on the definition of normality in this context?