titrasi redoks 2
DESCRIPTION
kimiaTRANSCRIPT
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.
Measurement of redox potentials permit detailed
analysis of complex enzyme mechanism
Electron path in multi-heme active site of P460
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 MnO4
- adalah:
E = (EFe3+/Fe2+ + 5EMnO4-/Mn2+)/6 – 0,08pH
Titrasi Redoks Bentuk kurva titrasi redoks
1.) Perubahan voltase sebagai fungsi penambahan titran Perhatikan reaksi titrasi (biasanya satu arah/sempurna). Misalnya:
Ce4+ di dalam buret diteteskan ke larutan Fe2+
Elektrode Pt mendeteksi konsentrasi relatif dariFe3+/Fe2+ & Ce4+/Ce3+
Elektrode calomel/SHE/dll digunakan sebagai reference
Eo = 0,68 V
Setengah reaksi pada elektrode Pt (reduksi – oksidasi):
K ≈
Eo = 1.44 V
Titrasi Redoks
Bentuk kurva titrasi redoks
2.) kurva titrasi memiliki tiga wilayah Sebelum titik ekivalen Pada titik ekivalen (TE) Setelah titik ekivalen
3.) Wilayah 1: sebelum titik ekivalen Tiap aliquot Ce4+ menghasilkan mol Ce3+
dan Fe3+ yang ekivalen
Kelebihan Fe2+ yang belum bereaksi berada dalam larutan
Jumlah Fe2+ dan Fe3+ dapat diketahui, digunakan untuk menghitung potensial sel.
Sisa Ce4+ tidak diketahui
Titrasi Redoks
Bentuk kurva titrasi redoks
3.) Wilayah 1: sebelum TE
Eo = 0.68 V
Use iron half-reaction relative to calomel reference electrode:
][
][log05916.068.0
3
2
Fe
FeE
Redox Titrations Bentuk kurva titrasi redoks
4.) Daerah 2: Pada titik ekivalen Enough Ce4+ has been added to react with all Fe2+
- Primarily only Ce3+ and Fe3+ present- Tiny amounts of Ce4+ and Fe2+ from equilibrium
From Reaction:
- [Ce3+] = [Fe3+]- [Ce4+] = [Fe2+]
Both Reactions are in Equilibrium at the electrode
][
][log05916.068.0
3
2
Fe
FeE
][
][log05916.044.1
4
3
Ce
CeE
Redox Titrations Shape of a Redox Titration Curve
4.) Region 2: At the Equivalence Point Don’t Know the Concentration of either Fe2+ or Ce4+
Can’t solve either equation independently to determine E+
Instead Add both equations together
][
][log05916.068.0
3
2
Fe
FeE
][
][log05916.044.1
4
3
Ce
CeE
][
][log05916.0
][
][log05916.044.168.02
4
3
3
2
Ce
Ce
Fe
FeE
Rearrange
][
][
][
][log05916.012.22
4
3
3
2
Ce
Ce
Fe
FeE
Add
Redox Titrations Shape of a Redox Titration Curve
4.) Region 2: At the Equivalence Point Instead Add both equations together
][
][
][
][log05916.012.22
4
3
3
2
Ce
Ce
Fe
FeE
][][
][][
24
33
FeCe
FeCeLog term is zero
VEVE 06.112.22
Equivalence-point voltage is independent of the concentrations and volumes of the reactants
Redox Titrations Shape of a Redox Titration Curve
5.) Region 3: After the Equivalence Point Opposite Situation Compared to Before the Equivalence Point
Equal number of moles of Ce3+ and Fe3+
Excess unreacted Ce4+ remains in solution
Amounts of Ce3+ and Ce4+ are known, use to determine cell voltage.
Residual amount of Fe2+ is unknown
Redox Titrations Shape of a Redox Titration Curve
5.) Region 3: After the Equivalence Point
Eo = 1.44 V
Use iron half-reaction relative to calomel reference electrode:
][
][log05916.044.1
4
3
Ce
CeE
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 curve
Titration curve for 2:1 Stoichiometry
2/3 height
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 titration
Redox Indicator is a chemical compound that undergoes a color change as it goes from its oxidized form to its reduced form
Redox Titrations Finding the End Point
2.) Redox Indicators Color Change for a Redox Indicator occurs mostly over the range:
where Eo is the standard reduction potential for the indicator and n is the number of electrons involved in the reduction
voltsn
.EE o
059160
V.to.volts.
.E 206108811
0591601471
V.to.).(V.to.)calomel(E.
.E 965084702410206108811
0591601471
For Ferroin with Eo = 1.147V, the range of color change relative to SHE:
Relative to SCE is:
Redox Titrations Finding the End Point
2.) Redox Indicators In order to be useful in endpoint detection, a redox indicator’s range of color
change should match the potential range expected at the end of the titration.
Relative to calomel electrode (-0.241V)
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 preoxidation
Reagents for prereduction or preoxidation must:- Totally convert analyte into desired form- Be easy to remove from the reaction mixture- Avoid interfering in the titration
Potassium Permanganate (KMnO4)- Strong oxidant- Own indicator Titration of VO2+ with KMnO4
Before Near AfterEquivalence point
Eo = 1.507 VViolet colorless
pH ≤ 1
Eo = 1.692 VpH neutral or alkaline
Violet brown
pH strolngly alkalineEo = 0.56 V
Violet green
Redox Titrations Common Redox Reagents
2.) ExampleA 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.