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  • 1. Kurva Titrasi Redoks Pendahuluan 1.) Titrasi Redoks Berdasarkan reaksi reduksi oksidasi antara analit dan titrant Banyak analit dalam lingkup kimia, biologi, lingkungan dan ilmu material dapat diukur menggunakan titrasi redoks.Electron path in multi-heme active site of P460Measurement of redox potentials permit detailed analysis of complex enzyme mechanism

2. PR 1. Buat kurva titrasi 25 ml Sn2+ 0,1 M dengan Ce4+ 0,1 M. Reaksi: Sn2+ + 2Ce4+ Sn4+ + 2Ce3+ 2. Tunjukkan bahwa potensial pada saat titik ekivalen untuk titrasi Fe2+ dengan MnO4adalah: E = (EFe3+/Fe2+ + 5EMnO4-/Mn2+)/6 0,08pH 3. Titrasi Redoks Bentuk kurva titrasi redoks 1.) Perubahan voltase sebagai fungsi penambahan titran Perhatikan reaksi titrasi (biasanya satu arah/sempurna). Misalnya: KCe4+ di dalam buret diteteskan ke larutan Fe2+Elektrode Pt mendeteksi konsentrasi relatif dari Fe3+/Fe2+ & Ce4+/Ce3+Elektrode calomel/SHE/dll digunakan sebagai reference Setengah reaksi pada elektrode Pt (reduksi oksidasi): Eo = 0,68 V Eo = 1.44 V 4. Titrasi Redoks Bentuk kurva titrasi redoks 2.) kurva titrasi memiliki tiga wilayah Sebelum titik ekivalen Pada titik ekivalen (TE) Setelah titik ekivalen3.) Wilayah 1: sebelum titik ekivalen Tiap aliquot Ce4+ menghasilkan mol Ce3+ dan Fe3+ yang ekivalenKelebihan Fe2+ yang belum bereaksi berada dalam larutanJumlah Fe2+ dan Fe3+ dapat diketahui, digunakan untuk menghitung potensial sel.Sisa Ce4+ tidak diketahui 5. Titrasi Redoks Bentuk kurva titrasi redoks 3.) Wilayah 1: sebelum TE Use iron half-reaction relative to calomel reference electrode: Eo = 0.68 V [ Fe 2+ ] E = 0.68 0.05916 log [ Fe 3+ ] 6. Redox Titrations Bentuk kurva titrasi redoks 4.) Daerah 2: Pada titik ekivalen Enough Ce4+ has been added to react with all Fe2+ -From Reaction: -Primarily only Ce3+ and Fe3+ present Tiny amounts of Ce4+ and Fe2+ from equilibrium[Ce3+] = [Fe3+] [Ce4+] = [Fe2+]Both Reactions are in Equilibrium at the electrode [ Fe 2+ ] E+ = 0.68 0.05916 log [ Fe3+ ] [Ce 3+ ] E+ = 1.44 0.05916 log [Ce 4+ ] 7. Redox Titrations Shape of a Redox Titration Curve 4.) Region 2: At the Equivalence Point Dont Know the Concentration of either Fe2+ or Ce4+ Cant solve either equation independently to determine E+ Instead Add both equations together [ Fe 2+ ] E+ = 0.68 0.05916 log [ Fe3+ ] [Ce 3+ ] E+ = 1.44 0.05916 log [Ce 4+ ] Add [ Fe 2+ ] [Ce 3+ ] 2 E+ = 0.68 + 1.44 0.05916 log [ Fe3+ ] 0.05916 log [Ce 4+ ] Rearrange [ Fe 2+ ] [Ce 3+ ] 2 E+ = 2.12 0.05916 log [ Fe3+ ] [Ce 4+ ] 8. Redox Titrations Shape of a Redox Titration Curve 4.) Region 2: At the Equivalence Point Instead Add both equations together [ Fe 2+ ] [Ce 3+ ] 2 E+ = 2.12 0.05916 log [ Fe 3+ ] [Ce 4+ ] [Ce 3 + ] = [ Fe 3 + ] [Ce 4 + ] = [ Fe 2 + ]Log term is zero2 E+ = 2.12V E+ = 1.06VEquivalence-point voltage is independent of the concentrations and volumes of the reactants 9. Redox Titrations Shape of a Redox Titration Curve 5.) Region 3: After the Equivalence Point Opposite Situation Compared to Before the Equivalence PointEqual number of moles of Ce3+ and Fe3+Excess unreacted Ce4+ remains in solutionAmounts of Ce3+ and Ce4+ are known, use to determine cell voltage.Residual amount of Fe2+ is unknown 10. Redox Titrations Shape of a Redox Titration Curve 5.) Region 3: After the Equivalence Point Use iron half-reaction relative to calomel reference electrode: Eo = 1.44 V [Ce 3+ ] E = 1.44 0.05916 log [Ce 4+ ] 11. Redox Titrations Shape of a Redox Titration Curve 7.) Asymmetric Titration Curves Reaction Stoichiometry is not 1:1 Equivalence point is not the center of the steep part of the titration curveTitration curve for 2:1 Stoichiometry2/3 height 12. Redox Titrations Finding the End Point 1.) Indicators or Electrodes Electrochemical measurements (current or potential) can be used to determine the endpoint of a redox titrationRedox Indicator is a chemical compound that undergoes a color change as it goes from its oxidized form to its reduced form 13. Redox Titrations Finding the End Point 2.) Redox Indicators Color Change for a Redox Indicator occurs mostly over the range:0.05916 E = Eo volts n where Eo is the standard reduction potential for the indicator and n is the number of electrons involved in the reductionFor Ferroin with Eo = 1.147V, the range of color change relative to SHE:0.05916 E = 1.147 volts = 1.088 to 1.206 V 1 elative to SCE is:0.05916 E = 1.147 E ( calomel ) = ( 1.088 to 1.206 V ) ( 0.241 ) = 0.847 to 0.965V 1 14. Redox Titrations Finding the End Point 2.) Redox Indicators In order to be useful in endpoint detection, a redox indicators range of color change should match the potential range expected at the end of the titration.Relative to calomel electrode (-0.241V) 15. Redox Titrations Common Redox Reagents 1.) Adjustment of Analyte Oxidation State Before many compounds can be determined by Redox Titrations, must be converted into a known oxidation state -This step in the procedure is known as prereduction or preoxidationReagents for prereduction or preoxidation must: -Totally convert analyte into desired form Be easy to remove from the reaction mixture Avoid interfering in the titrationPotassium Permanganate (KMnO4) -Strong oxidant Own indicatorTitration of VO2+ with KMnO4pH 1Eo = 1.507 V VioletcolorlesspH neutral or alkalineEo = 1.692 VVioletbrownpH strolngly alkalineEo = 0.56 V VioletgreenBefore Near After Equivalence point 16. Redox Titrations Common Redox Reagents 2.) Example A 50.00 mL sample containing La3+ was titrated with sodium oxalate to precipitate La2(C2O4)3, which was washed, dissolved in acid, and titrated with 18.0 mL of 0.006363 M KMnO4. Calculate the molarity of La3+ in the unknown.