In the titration of potassium dichromate () with acidified Mohr's salt solution, diphenylamine is commonly used as an indicator. Why does require an external indicator unlike ?

Question

In the titration of potassium dichromate ($K_2Cr_2O_7$) with acidified Mohr's salt solution, diphenylamine is commonly used as an indicator. Why does $K_2Cr_2O_7$ require an external indicator unlike $KMnO_4$?

Prashant Kotian · Accepted Answer

Correct answer: B. While changes sharply from intensely purple to colorless (making it a strong self-indicator), changes from orange to green. This transition is gradual and the mixed colors make it impossible to visually detect the exact end point, necessitating an external indicator like diphenylamine (which turns intense blue).

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