What is the oxidising agent in a manganate(VII) titration, and what is the oxidation state of the manganese in it?

The manganate(VII) ion MnO₄⁻ is the oxidising agent, and the manganese in it has oxidation state +7.

Why does a manganate(VII) titration need no added indicator?

MnO₄⁻ is intensely purple while Mn²⁺ is almost colourless, so the reagent indicates its own end point.

Describe what you see at the end point when MnO₄⁻ is run into acidified iron(II) solution.

The flask stays colourless or very pale until one drop gives a permanent faint pink colour.

Which acid is used to acidify a manganate(VII) titration, and why is hydrochloric acid avoided?

Dilute sulfuric acid is used, because manganate(VII) would oxidise the chloride ions of hydrochloric acid and the titre would be too large.

State the ionic equation for the reaction of manganate(VII) with iron(II) ions in acid solution.

The equation is MnO₄⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O.

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Developing Metals

Manganate(VII) titrations and their calculations

4 things to know
Components 01, 02 and 03

Overview

Recall questions on why manganate(VII) is self-indicating, which acid is used and why the others are not, and the calculations with iron(II), ethanedioate and peroxide.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

Why does a manganate(VII) titration need no indicator, and why are hydrochloric and nitric acid both unsuitable?

Numbers

What is the oxidising agent in a manganate(VII) titration, and what are its equations with iron(II) and with ethanedioate?

Numbers

Why is the ethanedioate titration warmed, what is the equation with hydrogen peroxide, and why is starch added late?

Numbers

Why is nitric acid also unsuitable for acidifying a manganate(VII) titration?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the oxidising agent in a manganate(VII) titration, and what is the oxidation state of the manganese in it?
Model answer
The manganate(VII) ion MnO₄⁻ is the oxidising agent, and the manganese in it has oxidation state +7.
2
Why does a manganate(VII) titration need no added indicator?
Model answer
MnO₄⁻ is intensely purple while Mn²⁺ is almost colourless, so the reagent indicates its own end point.
3
Describe what you see at the end point when MnO₄⁻ is run into acidified iron(II) solution.
Model answer
The flask stays colourless or very pale until one drop gives a permanent faint pink colour.
4
Which acid is used to acidify a manganate(VII) titration, and why is hydrochloric acid avoided?
Model answer
Dilute sulfuric acid is used, because manganate(VII) would oxidise the chloride ions of hydrochloric acid and the titre would be too large.
5
Why is nitric acid also unsuitable for acidifying a manganate(VII) titration?
Model answer
Nitric acid is itself an oxidising agent, so it would oxidise some of the reducing agent being measured and give a titre that is too small.
6
State the ionic equation for the reaction of manganate(VII) with iron(II) ions in acid solution.
Model answer
The equation is MnO₄⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O.

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