This document describes a potentiometric redox titration experiment to determine the percentage of iron in a sample. Key points: 1. The experiment involves titrating an iron solution with a standardized potassium permanganate solution while monitoring the electrode potential with a multimeter. 2. Graphs of voltage vs volume added are used to determine the equivalence point, from which the concentration of permanganate and percentage of iron can be calculated. 3. Results show the titration curves, first derivative plots used to find the equivalence point, and sample calculations determining 9.95x10-3M KMnO4 and 0.26% iron in the unknown sample.

1. Potentiometricredox titration Czarina Charmaine S. Diwa Ralph Marco S. Flores

2. Objectives: To construct a potentiometricredox titration curve Determine percent weight of iron in the sample

3. Potentiometricredox titration Introduction: Terms defined

4. Potentiometry A method of analysis based on measuring the potential of the electrochemical cells with a production minimal amount of current. One of the most used measurements because of its convenience. Aside from its applications on determining analyte concentrations, it is also used to determine thermodynamic equilibrium constants.

5. Redox (as in Redox reaction!) Reactions that require electrons to be transferred from one reactant to the other It is performed by bringing an oxidizing and reducing agents into direct contact in a container Or it is carried out in an electrochemical cell where the components are not in direct contact with each other

6. Titration A process wherein a standard reagent is added to a solution of an analyte until the reaction between the analyte and reagent is judged complete Completeness of the titration is based on the equivalence point, wherein the reagent is approximately equal to the analyte

7. Equipment and procedure

8. The equipments and important parts Multimeter/voltmeter – a device that measures the cell potential Reference electrode – a half-cell having a known electrode potential that remains constant and is independent of the analyte solution (Mohr’s salt solution) Indicator electrode – an electrode that varies as a result of the change in analyte concentration *together with the salt bridge and analyte solution, they constitute the electrochemical cell*

9. Methodology: preparation of the iron (III) solution Plug the end of a Pasteur pipet with cotton and soak it in a saturated solution of KCl or KNO3 Fill the pipet with 0.1 M CuSO4 and insert a copper wire. Dissolve pre-measured KMnO4 in 100mL dH2O and add enough dH2O to make 300 mL. Store in a colored container. Weigh 0.3 to 0.4 g Fe(NH4)2(SO4)2·6H2O and dissolve with 20 mL dH2O in a 100mL beaker. Add 5mL 2M H2SO4.

10. Methodology: Standardization of KMnO4 Dip the a carbon rod and the Cu/Cu2+ electrode in the prepared solution. Connect both electrodes to the multimeter. Add 2.0 mL of the KMnO4 solution into the Fe(NH4)2(SO4)2·6H2O + H2SO4 solution and measure the reduction potential (reading on the multitester). Repeat until 20 mL of KMnO4 solution has been added. Do not forget to stir after each addition. Add 1.0 mL KMnO4 solution until 30 mL KMnO4 solution has been added. Stir after addition. Plot the volume used versus the observed potential with the highest peak (in the first derivative plot) as the equivalence point.

11. Methodology: analysis of the unknown Pipet10mL of the unknown sample in a 100mL beaker. (pre-mixed with H2SO4) Add 2.0 mL of the KMnO4 solution into the unknown solution and measure the reduction potential (reading on the multitester). Repeat until 20 mL of KMnO4 solution has been added. Stir after each addition. Add 1.0 mL KMnO4 solution until 30 mL KMnO4 solution has been added. Stir after each addition. Plot the volume used versus the observed potential with the highest peak (in the first derivative plot) as the equivalence point. Calculate weight of Fe in the sample.

12. The electrochemical cell Reference electrode | salt bridge| analyte solution| indicator electrode

13. Results and discussion

14. Reactions involved: Standardization of potassium permanganate: Fe3+ + e- Fe2+ MnO4- + 5e- + 8H+  Mn2+ + 4H2O MnO4-+ 5Fe2+ + 8H+  Mn2++ 4H2O + 5Fe3+ Analysis of the unkown: MnO4-+ 5Fe2+ + 8H+  Mn2++ 4H2O + 5Fe3 Fe2+  Fe3+ + e- 5Fe2+  5Fe3+ + 5e-

15. Results: dE/dV titration curve

16. Results: 1st derivative plot

17. Results: 2nd derivative plot

18. Sample computation equivalence point: 20.5 mL weight of Fe(NH4)2(SO4)2.6H2O: 0.4g computation: M KMnO4 = (mass Fe)(molar mass Fe)(ratio)/(volume titrant) M KMnO4 = {[(0.4g Fe)/(392.14g Fe/mol Fe)][mol KMnO4 mol Fe]}/ .0205 L =9.95x10-3M KMnO4

19. Analysis of the unkown

20. Results: dE/dV titration curve

21. Results: 1st derivative plot

22. Results: 2nd derivative plot

23. Sample computation equivalence point: 9.5mL weight of Fe(NH4)2(SO4)2.6H2O: unkown computation: Xg Fe ={[9.5mL KMnO4][9.95-3M KMnO4][5 mol Feol KMnO4][(55.85g Fe/mol Fe)]} 0.0.02640 g =0.26% w/v

24. Some notes on: Indicator electrode: Cu2+/Cu Analyte: mohr’s salt Titrant: potassium permanganate

25. Sources of systematic errors Instrument error Multimeter Method error Photodecomposition of permanganate Acid error Personal error Detection of end point

26. Conclusion: Potentiometricredox titration An analytical process wherein a standard reagent is added to the analyte, one of which behaves as an electron donor and the other electron acceptor, until all analyte has been consumed, as judged by the change in the electrode potential.

27. End