Determination of concentration of KMnO₄ solution

 A. To determine of the strength of the given KMnO4 solution using standard oxalic acid solution

Materials Required

Real Lab Procedure

Preparation of standard solution of oxalic acid [250 ml M/10 (0.1 M) solution]

  •  Using an electronic balance, first weigh exactly 3.15g of oxalic acid crystals in a weighing bottle.
  • Transfer these into a 250ml beaker.
  • Then wash the weighing bottle 2 or 3 times with distilled water and transfer all the washings into the beaker.
  • Dissolve the oxalic acid crystals in the beaker by gentle stirring with a clean glass rod.
  • When the oxalic acid crystals in the beaker are completely dissolved, transfer the entire solution from the beaker into a 250ml standard flask through a funnel and a glass rod.
  •  Wash the beaker 2 to 3 times with distilled water and transfer all the washings into the standard flask.
  • Finally wash the funnel thoroughly with distilled water to transfer the drops of the solution on the sides of the funnel into the standard flask.
  •  Add enough distilled water to the standard flask so that the level is just below the calibration mark on it.
  • Add the last few drops of distilled water with a pipette until the lower level of the meniscus just touches the mark on the standard flask.
  •  Stopper the measuring flask and shake gently to make the solution uniform throughout.

Determination of strength of given KMnO4

  • Take a burette and wash it with distilled water.
  • Rinse and fill the burette with the given KMnO4 solution and set the initial burette reading as zero.
  • Clamp it vertically to the burette stand.
  • Rinse the pipette with water and then with the given oxalic acid solution.
  • Then pipette out 20ml of the given oxalic acid solution into a conical flask and add one test tube (~20ml) full of dil.H2SO4 into it.
  • Heat the contents of the conical flask to 60-70°C.
  • Titrate it against the KMnO4 solution taken in the burette till the colour of the solution in the conical flask changes from colourless to light pink.
  • Note down the final burette reading.
  • Repeat the titration until concordant values are obtained.

Observation

The readings are recorded in a tabular form as shown and the molarity of the given KMnO4 solution can be calculated using the molarity equation given in the theory.

SI. No Initial burette reading Final burette reading Volume of KMnO4 (in ml)
       
       
       
       

The Result

The strength of the given KMnO4 solution = ............g/litre

B. To determine the strength of the given KMnO4 solution using standard solution of Mohr’s salt

Materials Required

Real Lab Procedure

Preparation of standard solution of Mohr’s salt (Ferrous Ammonium Sulphate).[250 ml M/20 (0.05 M) solution]

  •  Using an electronic balance weigh exactly 4.9g of Mohr’s salt crystals in a weighing bottle.
  • Transfer these into a 250ml beaker.
  • Add 5ml conc.H2SO4 into the beaker.
  • Wash the weighing bottle well with distilled water and transfer all the washings into the beaker.
  • Dissolve Mohr’s salt crystals in the beaker by gentle stirring with a clean glass rod.
  • When the crystals in the beaker are completely dissolved, transfer the entire solution from the beaker into a 250ml standard flask through a funnel and a glass rod.
  • Wash the beaker thoroughly with distilled water and transfer all the washings into the standard flask.
  • Finally, wash the glass rod and the funnel thoroughly with distilled water to transfer the solution on the sides of the funnel into the standard flask.
  • Add enough distilled water to the standard flask so that the level is just below the calibration mark on it.
  • Add the last few drops of distilled water with a pipette until the lower level of the meniscus just touches the mark on the standard flask.
  • Stopper the measuring flask and shake gently to make the solution uniform throughout.

Determination of strength of KMnO4

  • Take a burette and wash it with distilled water.
  •  Rinse and fill the burette with the given KMnO4 solution and set the initial burette reading as zero.
  • Clamp it vertically to the burette stand.
  • Rinse the pipette with water and then with the given Mohr’s salt solution.
  • Pipette out 20ml of the given Mohr’s salt solution into a conical flask and add one test tube (~20ml) full of dil.H2SO4 into it.
  • Titrate it against the KMnO4 solution taken in the burette till the colour of the solution in the conical flask changes from colourless to light pink.
  • Note down the final burette reading.
  • Repeat the titration until concordant values are obtained.

Observation

The readings are recorded in a tabular form as shown and the molarity of the given KMnO4 solution can be calculated using the molarity equation given in the theory.

SI. No Initial burette reading Final burette reading Volume of KMnO4 (in ml)
       
       
       
       

The Result

The strength of the given KMnO4 solution = .............g/litre

Simulator Procedure (as performed through the Online Labs)

Titrate: Mohr's Salt

  • Select the titrate 'Mohr's Salt' from the 'Titrate' drop down list.
  • You can adjust the drops rate using the 'Drops rate' slider.
  • Use the respective sliders to select the molarity and volume of the titrate.
  • Drag the test tube containing Dil. H2SO4 to the conical flask to pour the solution in it.
  • Drag the conical flask and place it on tile.
  • Click on the 'Start' button or on the 'Nozzle' of the burette to start the titration.
  • The zoomed view of the burette reading is shown.
  • You can see the volume of KMnO4 used for the titration by clicking on the 'Show the volume of titrant' check box.
  • The end point is reached when a pink colour develops, at this point stop the titration either click on the 'Stop' button or click on the 'Nozzle' of the burette.
  • You can see the chemical equation of the reaction on the side menu.
  • Find out the number of moles of the titrate (n1) and that of the titrant (n2) from the chemical equation and enter the values in the respective text boxes and verify the values.
  • Calculate the molarity of the titrant using the given equation and enter the value in the corresponding text box and verify the value.
  • The molar mass of the titrant is shown on the side menu.
  • Calculate the strength of the given titrant (in g/lit) and enter the value in the corresponding text box and verify the result.
  • You can alternatively use the embedded worksheet to find the values by entering the data in the specific fields.
  • To redo the experiment click the 'Reset' button.

Note: Click on the ‘HELP’ button to see the instructions.

Titrate: Oxalic Acid

  • Select the titrate 'Oxalic Acid' from the 'Titrate' drop down list.
  • You can adjust the drops rate using the 'Drops rate' slider.
  • Use the respective sliders to select the molarity and volume of the titrate.
  • Drag the test tube containing Dil. H2SO4 to the conical flask to pour the solution in it.
  • Drag the conical flask and place it over the Bunsen burner.
  • Light the burner by clicking on the knob and heat it till the temperature reacher 70oC to 80oC.
  • Drag the conical flask and place it on tile.
  • Click on the 'Start' button or on the 'Nozzle' of the burette to start the titration.
  • The zoomed view of the burette reading is shown.
  • You can see the volume of KMnO4 used for the titration by clicking on the 'Show the volume of titrant' check box.
  • The end point is reached when a pink colour develops, at this point stop the titration either click on the 'Stop' button or click on the 'Nozzle' of the burette.
  • You can see the chemical equation of the reaction on the side menu.
  • Find out the number of moles of the titrate (n1) and that of the titrant (n2) from the chemical equation and enter the values in the respective text boxes and verify the values.
  • Calculate the molarity of the titrant using the given equation and enter the value in the corresponding text box and verify the value.
  • The molar mass of the titrant is shown on the side menu.
  • Calculate the strength of the given titrant (in g/lit) and enter the value in the corresponding text box and verify the result.
  • You can alternatively use the embedded worksheet to find the values by entering the data in the specific fields.
  • To redo the experiment click the 'Reset' button.

Note: Click on the ‘HELP’ button to see the instructions.

Precautions

  • Handle the apparatus and chemicals carefully.
  • Rinse the pipette and burette first with distilled water then with the corresponding solutions.
  • Close the pipette with the index finger.
  • Always keep the lower end of the pipette in the liquid when sucking it.
  • Do not blow out the last drop of the solution from the jet end of the pipette.
  • KMnO4 solution is always taken in the burette.
  • Avoid the use of burette having a rubber tap as KMnO4 reacts with rubber.
  • Carefully fill the burette with the solution and see that the stopcock does not leak.
  • Do not allow any air bubbles to remain inside the burette.
  • Read the upper meniscus while taking burette reading with KMnO4 solution.
  • Let no drops of solution be at the tip of the burette at the end point.
  • Add about an equal volume of dil.H2SO4 to the solution to be titrated before adding KMnO4.
  • If oxalic acid or some oxalate is to be titrated, add required amount of dil.H2SO4 and heat the flask to 60°-70°C.
  • In case of ferrous salt, no warming is required.
  • No external indicator is required for KMnO4 titration because KMnO4 acts as self indicator.
  • Do not rinse the titration flask with the solution.
  • Give a rotatory motion to the titration flask throughout the titration.
  • Place the titration flask containing solution on a white tile to see the colour change correctly. 

 

Cite in Scientific Research:

Nedungadi P., Raman R. & McGregor M. (2013, October). Enhanced STEM learning with Online Labs: Empirical study comparing physical labs, tablets and desktops. In Frontiers in Education Conference, 2013 IEEE (pp. 1585-1590). IEEE.

Cite this Simulator: