Lab 9 Redox Titration (Primary Standard)
(0.025 mol/l KMnO4)
Purpose: Part A:
1.
2.
To prepare a standard iron (II) solution using the primary standard, iron (II) ammonium sulfate
hexahydrate FeSO4(NH4)2SO4 * 6 H2O
To determine the molar concentration of an aqueous potassium permanganate, KMnO4 (aq) solution
doing a titration .
Purpose: Part B :
1.
Find the concentration of a hydrogen peroxide solution.
Prelab Exercise:
1.
Calculate the mass of FeSO4(NH4)2SO4 * 6 H2O required to make 100 mL of 0.0500 mol/L solution.
2.
Write the net ionic equation for the reaction of FeSO4(NH4)2SO4 * 6 H2O and KMnO4 in an acidic
solution.
Materials:
FeSO4(NH4)2SO4 * 6 H2O
1 scoop
1 weighing paper
eyedropper
400 mL beaker
pipet with bulb
2 100 mL beakers
stirring rod
10 mL graduated cylinder
50 mL beaker
100 mL volumetric flask
short stemmed funnel
250 mL Erlenmeyer flask
50 mL buret
3.0 mol/L H2SO4
KMnO4 solution
Unknown H2O2 solution
Procedure:
1.
2.
3.
4.
Ensure that all glassware is clean and dry
Use a scale to obtain the mass of FeSO4(NH4)2SO4 * 6 H2O determined in the prelab
Use a 100 mL beaker to obtain about 40 mL of 3.0 mol/L H2SO4
Transfer the FeSO4(NH4)2SO4 * 6 H2O to the beaker containing the acid. Stir the
mixture until all the solid has dissolved. Rinse the stirring rod into the beaker.
5. Use the funnel to transfer the FeSO4(NH4)2SO4 * 6 H2O solution from the beaker to
the volumetric flask. Rinse the beaker into the volumetric flask.
6. Use distilled water to dilute the solution to exactly 100 mL. Mix thoroughly by
inverting the volumetric flask several times.
7. Obtain about 70 mL of KMnO4 solution of unknown concentration in a 100 mL
beaker
8. Clean and rinse the 50 Ml buret and funnel with 2 or 3 5 mL portions of the KMnO4
solution. Fill the buret and record the initial buret reading of the permanganate
solution to the nearest 0.1 mL.
9. Rinse a 10 mL pipet with water and then with iron (II) solution from the volumetric
flask.
10. Pipet 10.0 mL of the standard iron (II) solution into a clean 250 mL Erlenmeyer flask.
11. Place a piece of white paper under the Erlenmeyer flask so the colour of the solution
can be seen better.
12. Titrate the sample of iron (II) solution with the MnO4- solution. Swirl the solution in
the flask to ensure complete mixing.
13. When a single drop brings about a faint persisting purple tinge in the liquid the
endpoint has been reached.
14. Record the final buret reading at endpoint.
15. Repeat steps 9-12 two more times.
16. When finished rinse all glassware with tap water.
Part B:
1. Use a clean, dry 100 mL beaker to obtain about 40 mL of hydrogen peroxide solution of
unknown concentration
2. Rinse a 10 mL pipet with distilled water than the H2O2 from the beaker.
3. Pipet 10.0 mL of H2O2 solution into a clean 250 mL Erlenmeyer flask.
4. Use a 50 mL beaker to obtain about 10 mL of 3.0 mol/L H2SO4
5. Use a 10 mL graduated cylinder to add about 3.0 mL of 3.0 mol/L H2SO4 to the H2O2 in
the flask
6. Use a 100 mL beaker to obtain about 75 mL of the MnO4- solution
7. Rinse and fill the buret with MnO4- solution. Record the initial buret reading
8. Titrate the H2O2 solution the previously standardized MnO4- solution. Record the final
buret reading.
9. Repeat steps 3-8 two more times
10. When finished, rinse out all glassware with water.
Observations:
Part A:
Trial 1
Trial 2
Trial 3
Trial 1
Trial 2
Trial 3
Volume of Fe2+(aq)
Final buret reading
Initial buret reading
Volume of KMnO4(aq)
used
Average volume of
KMnO4(aq)
Part B
Volume of H2O2(aq)
Final buret reading
Initial buret reading
Volume of KMnO4(aq)
used
Average volume of
KMnO4(aq
Calculations:
Part A:
1.
Using the balanced equation from the prelab exercise, determine the molar concentration of the potassium
permanganate solution. Use the average volume of KMnO4(aq)
Part B:
2.
Use the average volume of KMnO4(aq) used in Part B to determine the concentration of hydrogen peroxide
in the solution used in Part B.
3.
Determine the % W/V of the hydrogen peroxide solution. Compare your result to the % written on the
bottle.
Questions:
1.
What is the purpose of adding sulfuric acid to the Fe2+(aq) solution before titrating with KMnO4(aq)?
2.
In the procedure (Part B, step 1) instruction were to use a dry 100 mL beaker. Why is it important that the
beaker by dry?
3.
What chemical species serves to indicate the endpoint of these reactions?
Conclusion:
1.
2.
3.
4.
Summarize the lab in details.
Summarize your results.
Explain the sources of error
Describe the concepts that your learnt.