44. Titration based on redox reaction: permanganometry

Question 1

What is PERMANGANOMETRY?

Answer 1

a kind of titration where the strong oxidizing agent potassium permanganate (KMnO4) is used as the titrating agent.

Question 2

The goal of PERMANGANOMETRY

Answer 2

to determine the concentration of a solution containing a substance readily oxidized by KMnO4

Question 3

Composition of Potassium permanganate

Answer 3

s an ionic compound composed of K+ cations and MnO- (permanganate) an- 4
ions

Question 4

Color of MnO-4

Answer 4

a deep purple color both in 4

crystals and in solution

Question 5

Equation of Oxidation with potassium permanganate

Answer 5

In sufficiently acidic solutions MnO- can take up five electrons from the substance it oxidizes. MnO- is reduced to Mn2+

Question 6

the end point detection of permanganometry is based on what?

Answer 6

As Mn2+ ions are colorless this reaction is easily visualized by the disappearing purple color of MnO- . 4
=> If there’s no more oxidizable substance (e.g. oxalic acid or Fe2+) in the titrated solution the purple color of permanganate persists signaling the end of the titration.

Question 7

What is Oxalic acid

Answer 7

weak organic acid with the molecular formula C2H2O4

Question 8

Describe Reaction of potassium permanganate with oxalic acid

Answer 8

The complete oxidation of oxalic acid yields carbon dioxide

The reaction is slow at room temperature
=> have to heat up the reagents or add a catalyst

provide an acidic environment by adding a strong mineral acid such as H2SO4.

Question 9

Procedure of Titration of oxalic acid (PERMANGANOMETRY)

Answer 9

1. Fill your burette with 0.1N KMnO4.
2. Pipette 10 mL oxalic acid solution into three separate Erlenmeyer flasks.
3. Carefully add 10 mL 20% H2SO4 to each sample.
4. Heat one of the flasks to 100°C.
5. Let it cool down to approximately 60-70°C.
6. Slowly titrate KMnO4 to the solution. Don’t touch the glass! Use wooden tongs!
7. If the purple color of KMnO4 persists stop the titration and read the burette.
8. Repeat steps 4 – 7 with the remaining two flasks.

Question 10

What is Mohr’s salt (Fe2+)?

Answer 10

an inorganic ionic compound with the formula (NH4)2Fe(SO4)2

Question 11

Dissociation of Mohr’s salt

Answer 11

Mohr’s salt is an inorganic ionic compound with the formula (NH4)2Fe(SO4)2
=> dissociate in following ions

Question 12

Reaction of potassium permanganate with Mohr’s salt

Answer 12

The reaction will take place at room temperature with sufficient speed

A strong mineral acid will be required for providing an acidic environment.

Question 13

Procedure of Titration of Mohr’s salt (Fe2+)

Answer 13

1. Fill your burette with 0.1N KMnO4.
2. Pipette 10 mL Mohr’s salt solution into three separate Erlenmeyer flasks.
   The solution contains 20% H2SO4 so you don’t have to add it yourself. Pipette carefully!
3. Slowly titrate KMnO4 to the solution.
4. If the purple color of KMnO4 persists stop the titration and read the burette.
5. Repeat steps 3 – 4 with the other two flasks.