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Chemical Reactions

In the titrat...

Question

In the titration of $F e^{2 +}$ ions versus $C r_{2} O_{7}$ ions using diphenylamine as the internal indicator, phosphoric acid is added in the solution containing $F e^{2 +}$ ions. The role of phosphoric acid is to?

lower the value of

E^{\circ} (F e^{3 +}, F e^{2 +} | P t)

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raise the value of

E^{\circ} (F e^{3 +}, F e^{2 +} | P t)

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form complex with ferrous ions

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change the reduction potential involving the indicator

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Solution

The correct option is D change the reduction potential involving the indicator
${F e}^{+ 2}$ ion titration with ${C r}_{2} O_{7}^{- 2}$ using diphenyl amine as internal indicator. $H_{3} {P O}_{4}$ added in solution containing ${F e}^{+ 2}$ .
Role of phosphoric acid is added to mate complex with ${F e}^{+ 3}$ and move oxidation ${F e}^{+ 2}$ forward. Lowering ${F e}^{+ 3}$ , reduction potential change is increased. Hence endpoint is easily detected.
Hence, option $(D)$ is correct.

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