Learn about the preparation and standardization of 0.1 n potassium permanganate solution through a laboratory experiment or practical.
Aim:
To prepare and standardize 0.1 N KMnO4 solution using oxalic acid as primary standard.
Reference: Indian Pharmacopoeia (IP) 2014 Volume-1, Page No. 838
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade potassium permanganate (KMNO4), and oxalic acid (C2H2O4), etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.
Principle:
It is based on redox titration, which involves titrating an oxidizing agent with a reducing agent and vice versa to determine its strength. In acidic media, potassium permanganate works as a strong oxidizing agent that oxidizing oxalic acid to carbon dioxide. The known strength of oxalic acid is directly titrated with potassium permanganate to determine its strength. The endpoint of the titration is determined by the appearance of the permanent pink color and potassium permanganate act as a self-indicator. The following is the reaction that is involved in this titration.
The molecular weight of potassium permanganate (KMnO4) is 158 g/mol.
Preparation of 1 M sulphuric acid:
Take 54.00 ml of sulfuric acid (H2SO4) using a pipette, dilute in 1000 ml of distilled water in a volumetric flask, and properly mixing it.
Preparation of 0.1 N oxalic acid:
Take 6.3 mg of oxalic acid and dissolve in 100 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 1000 ml.
Preparation of 0.1 N potassium permanganate solution:
Take 3.2 g of potassium permanganate and dissolve in 1000 ml of distilled water in a volumetric flask, and properly mixing it. Then boil for 60 minutes on a water bath, let stand for 2 days, and then filter through a funnel with a glass wool plug. Keep the prepared solution in an amber color volumetric flask to protect it from light.
Titration procedure:
- All glassware should be cleaned and dried according to standard laboratory procedures.
- Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
- Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
- Remove air bubbles from the burette and adjust the reading to zero.
- Take 20.00 ml of prepared solution of oxalic acid and pour it into a conical flask.
- Add 5 ml of 1 M sulphuric acid and warm the solution mixture to about 700C.
- Titrate the sample solution with potassium permanganate solution until the endpoint is reached.
- When the solution is swirled for up to 10 seconds, a pink color appears and fades, indicates that the endpoint is approaching. The actual endpoint of the titration is indicated by a pink color that lasts longer than 30 seconds.
- To get accurate results, repeat the titration three times.
- Properly record the readings of the burette.
- Take their mean and calculate the molarity of sodium thiosulphate solution.
Calculations:
N1 V1 = N2 V2
N2 = V1 N1/V2
Where,
N2 is the normality of potassium permanganate solution
V1 is a volume of oxalic acid solution used
N1 is the normality of an oxalic acid solution
N2 is a volume of potassium permanganate solution used
Result:
The strength of the prepared potassium permanganate solution was found to be_____N.
Commonly asked questions on titration are as follows.
Which indicator is used in the standardization of potassium permanganate?
The endpoint of the potassium permanganate titration is determined by the appearance of the permanent pink color and KMnO4 acts as its own indicator due to its brilliant purple color.
Why do we standardize potassium permanganate solution?
Standardization of a prepared potassium permanganate solution is performed to determine its exact normality.
What are the different types of titration?
Titrations are classified as acid-base, redox, complexometric, precipitation based on the chemical reaction that occurs between the titrant and the analyte.
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