Lec_07 - Today 1. Report for Experiment 5 is due (40 pts)...

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Unformatted text preview: Today 1. Report for Experiment 5 is due (40 pts) 2. Post-lab for Experiment 5 is due (10 pts) 3. Pre-lab for Experiment 6 is due (5 pts) 4. Experiment 6. Synthesis and Analysis of a Complex Iron Compound. Part 2 have a write-up in your notebook Next scheduled week 1. Report for Experiment 6 is due (40 pts) 2. Post-lab for Experiment 6 is due (10 pts) 3. Pre-lab for Experiment 7 is due (5 pts) 4. Experiment 7(1). Synthesis and Analysis of a Complex Iron Compound. Part 3 have a write-up in your notebook Spring 2007 Experiment 6. Synthesis and Analysis of a Complex Iron Compound. Part 2 PURPOSE AND LEARNING OBJECTIVES To synthesize potassium oxalatoferrate coordination compound To use redox titration to determine the oxalate content of a prepared sample To use visible spectrophotometry to determine the iron content of a prepared sample To determine molecular stoichiometry of a synthesized sample using redox titration data in combination with the spectrophotometric data Kx[Fey(C2O4)x] zH2O Potassium content Water content Oxalate content Spring 2007 Iron content Volumetric Titrations A titration is a quantitative method of analysis in which the titrant is added to an analyte and the volume of the titrant required to complete the reaction is measured Titrant a reactant of known concentration Analyte a reactant of unknown concentration Measure: the volume of a titrant Determine: amount of an analyte Spring 2007 Redox Titration The chemical reaction = oxidation-reduction an electron transfer process takes place between an oxidizing agent and a reducing agent Oxidizing agent is a species that gets reduced during the reaction (gains electrons) Reducing agent is a species that gets oxidized during the reaction (loses electrons) Oxidation: loss of electrons Reduction: gain of electrons Example: Zn (s) + Cu2+ (aq) Zn2+ (aq) + Cu (s) Cu2+ + 2e Cu (s) oxidizing agent (gets reduced, gains electrons) Zn (s) Zn2+ + 2e reducing agent (gets oxidized, loses electrons) Spring 2007 Oxalate Content Determination by Redox Titration Potassium permanganate, KMnO4 oxidizing agent MnO4 titrant C2O42 analyte Oxalate, C2O42, in the synthesized compound (Kx[Fey(C2O4)x]zH2O) reducing agent We will use permanganate, MnO4, (titrant) to oxidize oxalate, C2O42, (analyte) The electron transfer will occur from the carbon in the oxalate ions to the manganese in the permanganate ions. electron transfer MnO4 (aq) + C2O42 (aq) Mn2+ (aq) + CO2 (g) reduction oxidation Spring 2007 Balancing the Redox Reaction Half reactions: 1. 2. Mn(+7)O4 + 8 H+ + 5e Mn2+ + 4 H2O 2 reduction half reaction oxidation half reaction C(+3)2O42 2 C(+4)O2 (g) + 2e 5 _______________________________________________ 2 MnO4 + 16 H+ + 10e 2 Mn2+ + 8 H2O 5 C2O42 10 CO2 (g) + 10e 1. 2. Overall balanced equation: 2 MnO4 + 16 H+ + 5 C2O42 2 Mn2+ + 8 H2O + 10 CO2 (g) Spring 2007 End Point KMnO4 has an intense purple color and serves as its own indicator The end point pale pink color appears and persists Pink color at the end point is due to the excess of KMnO4 end point As titration proceeds 2 MnO4 + 16 H+ + 5 C2O42 2 Mn2+ + 8 H2O + 10 CO2 (g) intense purple color part of Kx[Fey(C2O4)x]zH2O colorless Spring 2007 Example Calculation 2 MnO4 + 16 H+ + 5 C2O42 2 Mn2+ + 8 H2O + 10 CO2 (g) [KMnO4] = 0.0231 M VKMnO4 = 34.58 ml msample = 0.2187 g [C2O42] = ? (mole/g) At the equivalence point: 5 Moles of C 2O 2 - = Moles of MnO - 4 4 2 Moles of KMnO 4 = 0.0231 mole/L 34.58 ml = 0.000799 mole 1000 ml/L 5 Moles of C 2O 2 - = 0.000799 = 0.00200 moles 4 2 Moles of C 2O 2 - /g of sample = 4 0.00200 mole = 0.00913 mole/g 0.2187 g Spring 2007 Miscellaneous Tips Weigh the obtained crystals before proceeding with the titrations Use a 50:50 mixture of ethyl alcohol and water to wash the crystals Do not boil your titration mixture If it is too difficult to see the bottom of the meniscus in the burette, read the top of the liquid Do not use up all of your sample in titrations, you will need some (at least 0.15 g) for the next lab Perform additional trials if necessary until you obtain a consistent data set Spring 2007 ...
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This note was uploaded on 11/10/2008 for the course CH 204 taught by Professor Leytner during the Spring '08 term at University of Texas at Austin.

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