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Question

A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?


A

KMnO4 is an oxidising agent, it oxidises FeSO4

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B

FeSO4 acts as an oxidising agent and oxidises KMnO4

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C

The colour disappears due to dilution; no reaction is involved

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D

KMnO4 is an unstable compound and decomposes in the presence of FeSO4 to a colourless compound.

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Solution

The correct option is A

KMnO4 is an oxidising agent, it oxidises FeSO4


The explanation for the correct answer:-

Option (A) KMnO4 is an oxidising agent, it oxidises FeSO4

The reaction of Ferrous sulphate with acidified Potassium permanganate:-

  • When Ferrous sulphate FeSO4 is added to a beaker containing Potassium permanganate KMnO4, the products formed are Potassium sulphateK2SO4, Manganese(II) sulphateMnSO4, Ferric sulphate Fe2SO43and water.
  • The Complete balanced reaction involved is:

2KMnO4(aq)PotassiumpermanganatePurple+10FeSO4(aq)Ferroussulphate+8H2SO4(l)SulphuricacidK2SO4(aq)Potassiumsulphate+2MnSO4(aq)Manganese(II)sulphate+5Fe2(SO4)3(aq)Ferricsulphate+8H2O(l)Water

  • The oxidation state of Iron is FeSO4is +2, but in Fe2SO43 the oxidation state of Iron is +3, thus it gets oxidised.
  • This is because here KMnO4 acts as a strong oxidising agent, and it oxidises Iron in the presence of Sulphuric acid.
  • The purple colour of the solution which was due to KMnO4, now slowed turn colourless as all the KMnO4 is utilized.
  • Hence it is the correct option.

The explanation for incorrect answers:-

Option (B) FeSO4 acts as an oxidising agent and oxidises KMnO4

  • In this above reaction KMnO4 acts as a strong oxidising agent and oxidises Iron.
  • FeSO4does not act as a strong oxidising agent.
  • Hence it is the incorrect option.

Option (C) The colour disappears due to dilution; no reaction is involved

  • The colour disappears due to the complete utilization of KMnO4.
  • The complete reaction is:

2KMnO4(aq)PotassiumpermanganatePurple+10FeSO4(aq)Ferroussulphate+8H2SO4(l)SulphuricacidK2SO4(aq)Potassiumsulphate+2MnSO4(aq)Manganese(II)sulphate+5Fe2(SO4)3(aq)Ferricsulphate+8H2O(l)Water

  • Hence it is the incorrect option.

Option (D) KMnO4 is an unstable compound and decomposes in the presence of FeSO4 to a colourless compound

  • KMnO4 is a strong oxidising agent and a stable compound.
  • It oxidises FeSO4to Fe2SO43.
  • The purple colour disappears due to the complete utilization of KMnO4in this oxidising process.

Therefore, option (A) KMnO4 is an oxidising agent, it oxidises FeSO4 is the correct statement.


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