Chemistry · The chemistry involved in the titrimetric exercises: acids, bases and the use of indicators, oxalic-acid vs KMnO4, Mohr's salt vs KMnO4

In the titration of ferrous ammonium sulphate and potassium dichromate, the exte

In the titration of ferrous ammonium sulphate and potassium dichromate, the external indicator used is:

  • A. \( K C N S \)
  • B. \( N H_{4} C N S \)
  • C. \( K_{3}\left[F e(C N)_{6}\right] \)
  • D. \( K_{4}\left[F e(C N)_{6}\right] \)

Step-by-step solution

In the titration of ferrous ammonium sulphate with potassium dichromate, the external indicator used is potassium ferricyanide (K3[Fe(CN)6]). It reacts with Fe²⁺ ions to form a blue precipitate of Prussian blue. The endpoint is reached when all Fe²⁺ is oxidized and no blue color appears upon testing a drop of the solution with the indicator.
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