What is the normality of the following solution?

Consider the following unbalanced redox reaction:
Cr2O27+Fe2++H+Cr3++Fe3++H2O

What is the normality of a K2Cr2O7 solution, 35.0 cm3 of which contains 3.87g of K2Cr2O7
I am struggling to work out the equivalent weight. I have no idea how to get it.

1 Answer
Mar 22, 2018

Well, by definition, molarity=moles of solutevolume of solution

Explanation:

And so...3.87g294.18gmol135.0cm3×103Lcm3=0.376mol

And so nCr2O27=0.376mol

As regards equivalence, we need to write the appropriate redox reaction, for which we use the method of half-equations...

Orange dichromate, Cr(VI+), is reduced to green Cr3+:

Cr2O27+14H++6e2Cr3++7H2O(l) (i)

And ferrous ion is OXIDIZED to ferric ion...

Fe2+Fe3++e (ii)

And clearly, to balance, we take (i)+6×(ii)...and cancel common reagents....we add the equations in these mulitples in order to remove the electrons are virtual particles of convenience....

Cr2O27+6Fe2++14H++6e6Fe3++2Cr3++7H2O(l)+6e

Cr2O27+6Fe2++14H+6Fe3++2Cr3++7H2O(l)

Now you have the molar equivalence of Fe(II)....16equivCr2O271equivFe2+.

Does this help you?