Publication No. 12972
Laboratory Kit for AP® Chemistry
Materials Included In Kit
Ferrous ammonium sulfate, Fe(NH4)2(SO4)2•6H2O, 50 g
Manganese sulfate, MnSO4•H2O, 1.0 M, 100 mL
Oxalic acid, H2C2O4, 0.25 M, 100 mL
Potassium permanganate, KMnO4, 0.10 M, 500 mL
Sulfuric acid, H2SO4, 6 M, 1 L
Additional Materials Required
Beakers, 100-mL, 36
Burets, 50-mL, 12
Erlenmeyer flask, 250-mL, 36
Graduated cylinders, 10-mL, 12
Hot plates, 6
Ring stands and buret clamps, 12
Volumetric pipets, 10-mL, 12
Volumetric pipets, 25-mL, 12
Wash bottles, 12
Fe2+ standard solution, 0.100 M (Make fresh day of laboratory.)
To prepare 1 liter of solution
To prepare 1 liter of solution
Sulfuric acid (6 M) is corrosive to eyes, skin, and other tissue; always add acid to water, never the reverse. Potassium permanganate solution may be a skin irritant. The oxalic acid solution is a skin and eye irritant; it is moderately toxic by ingestion. The manganese sulfate solution is a body tissue irritant. Wear chemical splash goggles and chemical-resistant gloves and apron. Have students wash their hands thoroughly with soap and water before leaving the laboratory. Please consult current Safety Data Sheets for additional safety information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The potassium permanganate solution may be disposed of according to Flinn Suggested Disposal Method #12a. The Part 1 and 2 titration solutions and the manganous sulfate solution may be disposed of according to Flinn Suggested Disposal Method #27f. The 6 M sulfuric acid solution may be disposed of according to Flinn Suggested Disposal Method #24b. The oxalic acid and its solution may be disposed of according to Flinn Suggested Disposal Method #24a. The ferrous ammonium sulfate may be disposed of according to Flinn Suggested Disposal Method #26a; its solution by #26b.
AP Chemistry Standards
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesAsking questions and defining problems
Developing and using models
Planning and carrying out investigations
Analyzing and interpreting data
Using mathematics and computational thinking
Engaging in argument from evidence
Disciplinary Core IdeasHS-PS1.A: Structure and Properties of Matter
HS-PS1.B: Chemical Reactions
Cause and effect
Scale, proportion, and quantity
Systems and system models
Energy and matter
Stability and change
HS-PS1-1. Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
Answers to Prelab Questions
Molarity of MnO4- solution: 0.0206 M
Molarity of H2C2O4 solution: 0.0260 M
Answers to Questions
A common task in analytical chemistry is the determination of the amount of a substance present in a sample or product. If the product contains a substance that can be oxidized, then it is possible to determine the number of moles of that substance by titrating the sample with a solution of a strong oxidizing agent. In this lab, an oxidizing solution will be standardized and then use to determine the number of moles of oxalic acid, a reducing agent.
Oxidation–reduction reactions occur by electron transfer. The balanced chemical reaction can be written as the combination of two half-reactions, representing the oxidation reaction and the reduction reaction, respectively.
In this experiment, potassium permanganate, KMnO4, is used as the oxidizing agent. In an acidic solution, the MnO4 – ion is reduced from Mn(VII) to Mn(II) according to the following half-reaction:
In Part 1, a solution of KMnO4 is standardized by titration with a solution containing a known concentration of iron(II) ions, (Fe2+).
In the corresponding oxidation half-reaction, the Fe2+ ion is oxidized to Fe3+:
Combining half-reactions 2 and 3 and balancing the number of electrons transferred gives the overall reaction equation:
The balanced equation shows that 5 moles of Fe2+ are required to react with 1 mole of MnO4–.
For this redox titration, the equivalence point occurs when the exact number of moles of Fe2+ ions has been added to react completely with all the MnO4– ions in solution. At this point:
If the volume and molarity of the Fe2+ solution are known, then:
Rearranging Equation 2 yields the equation for the concentration of the potassium permanganate solution.
The indicator for this titration is the MnO4– ion itself. The MnO4– ion is purple in solution. At the endpoint of the titration, the solution changes from light pink to colorless.
In Part 2, the concentration of an oxalic acid solution is determined by titration with the permanganate solution standardized in Part 1. In this case, the endpoint occurs when the pink color of the MnO4– ion persists. The half-reaction for the oxidation of oxalic acid is:
The oxidation state of carbon changes from (+3) in H2C2O4 to (+4) in H2CO3.
The purpose of this lab is to standardize a solution of potassium permanganate by redox titration with a standard solution of iron(II) ions. A solution of oxalic acid is then titrated with the permanganate solution to determine the exact concentration of oxalic acid.
Ferrous ammonium sulfate, Fe(NH4)2SO4•6H2O, 0.100 M, 50 mL
Manganese sulfate, MnSO4•H2O, 1.0 M, 5 mL
Oxalic acid solution, H2C2O4, 60 mL
Potassium permanganate, KMnO4, ≈0.02 M, 100 mL
Sulfuric acid, H2SO4, 6 M, 50 mL
Water, distilled or deionized
Erlenmeyer flasks, 250-mL, 3
Graduated cylinder, 10-mL
Volumetric pipet, 10-mL
Volumetric pipet, 25-mL
Sulfuric acid (6 M) is corrosive to eyes, skin, and other tissue; always add acid to water, never the reverse. Potassium permanganate solution may be a skin irritant. The oxalic acid solution is a skin and eye irritant; it is moderately toxic by ingestion. The manganese sulfate solution is a body tissue irritant. Wear chemical splash goggles and chemical-resistant gloves and apron. Wash hands thoroughly with soap and water before leaving the laboratory.
Part 1. Standardization of a Potassium Permanganate Solution
Student Worksheet PDF