Name____________________________________________ Date__________
IB score ___________ = AISG score ____________%
Determination of Percentage Iron Content by Redox Titration
Assessed for: DCP and CE, along with MS as always
Grading will be done with the AISG IA Chemistry rubric, which follows the IB IA criteria.
Introduction:
Compounds containing iron in the +2 oxidation state can be measured by redox titration with a
strong oxidizing agent.
Potassium permanganate is a strong oxidizing agent that will be reduced and will oxidize iron (II)
in an acidic solution to form iron (III) and manganese (II) ions.
MnO4- + Fe2+ → Mn2+ + Fe3+ (acidic conditions)
Purple
colorless
Permanganate ion indicates the titration endpoint when a faint red/pink color persists in the solution
indicating all of the iron (II) has been used up.
Purpose:
Use a standardized solution to measure the percentage iron content in an unknown iron salt.
Materials:
KMnO4 (aq) potassium permanganate (0.0200 mol dm-3)
analytical balance
unknown iron (II) salt
50 mL graduated cylinder
3 mol dm-3 H2SO4 (aq)
funnel
titration burette
ring stand and burette clamp
125 mL Erlenmeyer flask
distilled water
Safety:
Sulfuric acid is a skin/eye irritant wash spilled area with water
KMnO4 solution will stain skin and clothes purple
Burette fills fast and will spill over top.
Wear gloves as permanganate will oxidize your skin very quickly.
Procedure:
1. Weigh 0.45_ _ g of unknown iron salt on an analytical balance. This balance is in the lab
room. Carry your salt carefully so it doesn’t spill.
2. Dissolve the unknown in a 50 mL beaker with 15 mL of 3 mol dm-3 sulfuric acid and 25 mL
distilled water.
3. Properly condition your burette with the titrant. Run a rough titration to determine the
approximate volume of titrant needed.
4. Carefully titrate permanganate solution in your burette to the beaker to the pink endpoint
that persists for at least 30 seconds.
5. Complete 4 total trials. Watch to make sure you do not run out of the solution in the burette.
6. Clean up.
7. Complete the necessary calculations and data analysis to address the purpose of this lab.
Once you have shown your calculations to your instructor, get the actual value of the % iron.
8. Write a conclusion and evaluation. Use the IB Chemistry Guide to help you determine what
should be included in your conclusion and evaluation section.
Basic tips:
The purple permanganate in the burette will disappear in analyte as it oxidizes the Fe 2+ to
Fe3+. What will happen to the color of the analyte when there is no more Fe2+ to convert? (pink
color will persist). Many color changes will occur as iron and permanganate all have different
oxidation state colors and combinations. Since the solution is dark, you can read the top of the
meniscus, this is acceptable, because we are getting the difference in the value, so if you remain
consistent, it doesn’t matter.
Permanganate is hard to read, so use the top of the meniscus EACH
time!
Rough titration can end with very pink
Trials should have light pink color that lasts 30 seconds