Titration of Oxygen Bleach
Overview:
You will use a redox titration to determine the hydrogen peroxide concentration in two solutions. One
will be a standard prepared according to reaction (1) below and the other will be a sample of color-safe
bleach purchased at Bilo.
Reactions:
For preparation of the standard:
(1) 2H2O + BO3- → H2O2 + H2BO3For titration of the bleach:
(2) 5H2O2 + 2MnO4- + 6H+ → 5O2 + 2Mn2+ + 8H2O
Procedure:
Titrate a standard sample:
1. Determine the moles of H2O2 required to react with 10.0 ml of 0.0100 M KMnO4.
2. Determine the mass of NaBO3 * 4H2O required to produce the moles of H2O2 calculated in #2 (refer to
reaction equation (1)).
3. Prepare a solution that will work to act as a stock solution to prepare at least three smaller samples to be
titrated by the KMnO4 solution. Remember, you want to use no less than 10.0 ml for each titration so if
you use the amount of NaBO3 * 4H2O that you calculated in step #3, you’ll only be able to use about 10
ml of the 0.0100 M KMnO4 in 1 titration. You need to have enough solution to be able to do three
titrations.
4. Place the amount of prepared H2O2 standard you determine to be appropriate into an Erlenmeyer flask
and add an equal volume of 1.0 M H2SO4. You must carefully determine the volume of the H2O2
standard. Calculate the number of moles of H2O2 present in the solution you are about to titrate.
5. Fill the buret with the KMnO4 solution.
6. The reaction that occurs in the titration is catalyzed by the Mn2+ produced by the reaction so the initial
pink color will fade rather slowly. Add about 1 ml of titrant from the initial volume and wait until the
pink color goes away. Continue titrating the sample at this point until the pink remains. Repeat the
titration at least twice. If your results are not consistent do a third titration.
7. Calculate the moles of KMnO4 added to reach the end-point for each titration.
8. Calculate the mole ratio of KMnO4 to H2O2 and compare your results to the accepted value from the
balanced reaction equation.
Titrate the bleach sample:
1. Prepare the bleach sample by adding 10.0 ml of bleach to a flask or cylinder and adding water to reach a
total volume of 100.0 ml.
2. Add 10.0 ml of the diluted bleach to a flask along with 20 ml of 1.0 M H2SO4.
3. Titrate the bleach using the MnO4- solution.
4. Repeat the titration at least twice (if time permits).
5. Determine the % by mass H2O2 in the bleach. Remember to account for the fact that you diluted the
original bleach sample. Assume the density of the bleach is 1.0 g/ml
Follow up:
1. Discuss your results for each set of titrations.
2. If you do not precisely measure the volume of the H2O2 standard in step #5, how will your
results be affected? Why is it not important to precisely measure the volume of the 1.0 M
H2SO4 in that same step of the procedure?
Complete these Free Response Questions:
2010B #3, 2003B #5 + additional calculations below, 2007#5
AP FR 2003B #5 Additional Calculations:
a)
The student dissolved 0.125 g of oxalic acid to make the solution in the flask. Determine the number of
moles of oxalic acid:
b) Use the balanced reaction to determine the moles of permanganate ion that reacted with the oxalic acid:
c) Determine the molarity of the permanganate ion if 25.00 ml of permanganate solution was used:
d) What mass of KMnO4 would have to be used to produce 2.5 L of the solution with the same molarity
used in the buret?
e) Write the balanced ½ reaction for the oxidation part of this reaction.
Report Sheet for Bleach Titration
Name:
1. Moles of H2O2 that will react with 10.0 ml of 0.0100 M KMnO4
2. Mass of NaBO3 * 4H2O required to produce moles of H2O2 from calculation #2
3. Describe:
a) Preparation of the stock H2O2 solution
b) The titration of the prepared standard H2O2
4. Moles of H2O2 present in the solution you titrated
5. Moles of KMnO4 added to reach the end point
6. Mole Ratio of MnO4- to H2O2 from data
7. Mole Ratio of MnO4- to H2O2 from reaction
8. Comparison of experimental and theoretical mole ratio
9. Mass of bleach titrated (account for dilutions)
10. Moles of MnO4- used to titrate bleach sample
11. Mass of H2O2 in bleach sample
12. % by mass H2O2 in bleach
Attach answers to follow up questions.