Question

A solution containing \[F{{e}^{2+}}\] ions is titrated with \[KMn{{O}_{4}}\] solution. Indicator used will be:
A. Phenolphthalein
B. Methyl orange
C. Litmus
D. None of the above

Answer 1

Hint: In order to solve this question, write the equation for reaction of iron (II) with potassium permanganate in acidic conditions. It will undergo a redox reaction, where iron gets oxidized and permanganate gets reduced.

Complete step by step answer:
According to the question, a titration is carried out and the reaction occurs as –
\[5F{{e}^{+2}}+MnO_{4}^{-}+8{{H}^{+}}\to 5F{{e}^{+3}}+M{{n}^{+2}}+4{{H}_{2}}O\]
As we can see, this is an acid base titration. \[F{{e}^{+2}}\]reacts with permanganate in acid medium to undergo an oxidation–reduction or redox reaction, where permanganate is the oxidizing agent and \[F{{e}^{+2}}\] is the reducing agent.
Potassium permanganate\[(KMn{{O}_{4}})\] is a very strong oxidizing agent. Permanganate\[(MnO_{4}^{-})\] has a very dark purple color.
As we can see in the given reaction, permanganate gets reduced. As a result of this, the purple permanganate changes its colour to colorless. The colour of the solution turns from dark purple to a faint pink colour at the equivalence point.
Hence, no additional indicator is required for this titration.
Therefore, the answer is – option (d) – None of the above.

Additional Information:
Potassium permanganate\[(KMn{{O}_{4}})\] is also known as a self-indicator.

Note: Titration is defined as, “a technique in which a solution of known concentration is used to determine the concentration of an unknown solution”. In this, the titrant (the known solution) is added from a burette to a known quantity of the analyte (the unknown solution) until the equivalence point is reached.