Question
Chemistry Question on Electronic Configurations Of Elements And The Periodic Table
In the titration of Fe2+ ions versus Cr2O72– ions using diphenylamine as the internal indicator, phosphoric acid is added in the solution containing Fe2+ ions. The role of phosphoric acid is to
A
(A) lower the value of Eo (Fe3+, Fe2+|Pt)
B
(B) raise the value of Eo (Fe3+, Fe2+|Pt)
C
(C) form complex with ferrous ions
D
(D) change the reduction potential involving the indicator
Answer
(A) lower the value of Eo (Fe3+, Fe2+|Pt)
Explanation
Solution
Explanation:
The reduction reaction to be considered is Fe3+(aq)+e−⟶Fe2+(aq)Its Nernst equation is:E=E0−RTFln[Fe2+][Fe3+]The addition of phosphoric acid forms the complex with ferric ion and thus lowers its concentration. Hence, the reduction potential becomes more negative.