help on another tough normality question

[Smooth Operater]

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The normality of a potassium permanganate solution is
2.10. What is the molarity of the solution if in the
course of the reaction the potassium permanganate is
changed to manganese dioxide?

A. 0.30
B. 0.70
C. 2.10
D. 6.30
E. 10.50

I am getting owned on the normality question. I am very clueless about how to arrive to the right answer which is B even after looking at kaplan's solution.

Hope someone can explain to me. Thanks!

 

[aranjuez]

Where are you finding these questions in Kaplan? I don't remember seeing them...

KMnO4 -> MnO2 is a reduction. 3 e- difference.

2.10m/3e- = 0.7

aranjuez

 

[busdent]

Manganese oxidation goes from +7 to +4 and thats accounts for the 3e-

 

[Smooth Operater]

thanks guys,

this question is from Natural Science Workshop B

Kaplan says to find the molarity, we go "2.10N/3e- = 0.7". But Why?? I know 3 e is released. How can you convert from N to molarity by dividing 3 e? What's the logic behind it?

Thanks!

 

[dudewhensmydat]

thanks guys,

this question is from Natural Science Workshop B

Kaplan says to find the molarity, we go "2.10N/3e- = 0.7". But Why?? I know 3 e is released. How can you convert from N to molarity by dividing 3 e? What's the logic behind it?

Thanks!

Dude, each proton has 1 e-, giving you 3 e-. Remember that normality is a colligative property (so you just count the number of protons a compound can give away and keep in mind the molarity/M as well).

I hope I'm right on this one.

 

[Manyak222]

Yes, Normality describes the number of reactive species, which could be protons, hydroxides, electrons, etc. molarity = normality/#of reactive species.

Dude, each proton has 1 e-, giving you 3 e-. Remember that normality is a colligative property (so you just count the number of protons a compound can give away and keep in mind the molarity/M as well).

I hope I'm right on this one.