New York, NY IMG HI 58° LO 56° Home About Contact
Home Chemistry Engineering Chemistry Estimation of Fe2+ ion by Potentiometry using KMnO4 Titrations
Engineering Chemistry Lab Experiments

Estimation of Fe2+ ion by Potentiometry using KMnO4 Titrations

Title of Experiment: Estimation of Fe2+ ion by Potentiometry using KMnO4 Titrations


To estimate the amount of ferrous iron present in the whole of the given solution by potentiometry.


The total reaction is

2KmnO4 + 8H2SO4 + 10FeSO4 ————> K2SO4 + 2MnSO4 + 5Fe2(SO4)3 + 8H2O

Preperation of Solution

1. Preparation of standard KMnO4:

Dissolve 1.58gm of KMnO4 in 1000 ml of distilled water and shake the flask well for uniform concentration. Because KMnO4 is a secondary standard, it is standardized by titrating with standard oxalic acid.

2. Preparation of standard oxalic acid solution:

Weigh out accurately 0.315gms of oxalic acid crystals into a 100ml standard flask, dissolve the sample in little distilled water and make up the solution to the mark distilled water and shake the flask well for uniform concentration.

3. Preparation of 2N H2SO4 solution:

56ml of conc.H2SO4 is added Drop by Drop to 1000ml of water taken in a beaker by keeping it in a trough of water. This reaction is highly exothermic.

Note: H2SO4 must not be added to water.


Standardization of KMnO4 solution:

Pipette out 20ml of the oxalic solution into a 250ml conical flask and add 20ml of 2N H2SO4. Heat the solution to 70 – 80 ͦ C. (till fumes come out of the solution) and titrate the warm solution with KMnO4 taken in a burette. The end point is pale pink color. Note the burette reading and repeat the titration for concurrent values.

Let the titre value be xml.

V1 N1 = V2 N2

V1 = Volume of oxalic acid
V2 = Volume of KMnO4
N1 = Normality of oxalic acid
N2 = Normality of KMnO4
(N2) Normality of KMnO4 = 20 * Normality of Oxalic acid / x

Potentiometric Titration

The given Fe2+ solutions is made up to the mark of the given 100 ml standard flask and shake the flask well for uniform concentration. Pipette out 20ml of the Fe2+ solution into a clean 250ml beaker and add equal volume(20 ml ) of dil. H2SO4 along with 100ml of distilled water to enable the electrodes to immerse well in the solution. A platinum electrode ( indicator electrode) and a standard calomel electrode ( reference electrode) from the potentiometer are dipped in to the beaker. The solution in the beaker is stirred using a magnetic stirrer. The initial EMF is noted 0.5 ml of KMnO4 solution is added from the burette at regular intervals of time, while stirring the solution and the EMF is measured. The volume of KMnO4 added and the corresponding EMF readings are noted. At the end point there is a sharp increase in EMF due to the complete oxidation of the Fe2+ to Fe3+. The addition of KMnO4 is continued till the equivalent point is crossed by at least 5ml.

From the observed values:
ΔE= E2 – E1
ΔV= V2 – V1
ΔE /ΔV is calculated for each addition of KMnO4 and a graph is drawn by pointing ΔE /ΔV (y-axis) against volume of KMnO4 added (x axis). A smooth curve is drawn by joining all the points. The peak in the graph indicates the end point as shown below. From the amount of Fe+2 is calculated.


V2 N2 = V3 N3
V2 = Volume of KMnO4
N2 = Normality of KMnO4
V3 = Volume of Fe+2
N3 = Normality of Fe+2

N3 = y (20 * Normality of KMnO4) / 20


Amount of Fe+2 present in the given solution = (N3 * equvivalent wt) / (N3 * 55.85 gms/100ml)

Viva Questions and Answers

  1. What is redox reaction?
  2. What is the example for strong oxidizing agent?
  3. What is the reaction occurs between ferrous ion and ferric ion?
  4. What is relation between Molarity and Normality?
  5. Define Normality?