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REDOX TITRATIONS

REDOX TITRATIONS. REDOX Titrations. A redox titration is used to determine the concentration of an oxidizing or reducing agent.

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REDOX TITRATIONS

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  1. REDOX TITRATIONS

  2. REDOX Titrations • A redox titration is used to determine the concentration of an oxidizing or reducing agent. • The reaction needs to have a 100% yield (go to completion – no excess of either reactant) and there needs to be a color change to indicate when the reaction is complete. Indicators can be used but often there is a color change when one of the reactants undergoes oxidation or reduction (and that serves as the indicator).

  3. Example #1 KMnO4 (aq) reacts with oxalic acid, H2C2O4, in acidic solution by the reaction: 5 H2C2O4 (aq) + 2 MnO4-1 (aq) + 6 H+1 (aq)  10 CO2 (g) + 2 Mn+2 (aq) + 8 H2O (l) 0.2585 g of oxalic acid is dissolved in approximately 100 mL of 0.5 M H2SO4. Upon titration with KMnO4 and adding 22.35 mL, a faint purple color persists indicating the reaction is complete. What is the concentration of the KMnO4 solution?

  4. ? M 0.2585 g 22.35 mL 5 H2C2O4(aq) + 2 MnO4-1(aq) + 6 H+1(aq)10 CO2(g) + 2 Mn+2(aq) + 8 H2O (l) whenever you are finding an M value, you must start with a fraction (because M is a fraction) AND the bottom of the fraction needs to be the volume in liters of THAT solution = 0.0514 M MnO4-1

  5. Example #2 The concentration of aqueous I3-1 solution can be determined by titration with aqueous sodium thiosulfate, Na2S2O3. We can use a starch indicator, which turns from deep blue to colorless when all the I3-1 has reacted. What is the molar concentration of I3-1 if 24.55 mL of 0.102 M Na2S2O3 is needed for complete reaction with 10.00 mL of the I3-1 solution?

  6. 0.102 M ? M 24.55 mL 10.00 mL 2 S2O3-2 (aq) + I3-1 (aq)  S4O6-2 (aq) + 3 I-1 (aq) * = 0.125 M I3-

  7. Example #3 Normal range of Ca+2 ion in human blood is 9.0 - 11.5 mg of Ca+2 in 100 mL of blood. Abnormal levels (high and low) are indicative of several diseases. 1.00 mL of blood is treated with Na2C2O4 to precipitate calcium as CaC2O4. The precipitate is isolated and dissolved in H2SO4. This solution is titrated with 4.88 x 10-4 M KMnO4. 2.05 mL KMnO4 required to reach the end point (faint violet color remains). (a) How many mg calcium (Ca+2) are in 100 mL of this blood? (b) If the 1 mL of blood has a mass of 1.060 g, what is the mass % of the Ca?

  8. (a) How many mg calcium (Ca+2) are in 100 mL of this blood? .000488 M 2.05 mL ? mg 2 KMnO4(aq) + 5 CaC2O4(aq) + 8 H2SO4(aq)  2 MnSO4(aq) + K2SO4(aq) + 5 CaSO4(aq) + 10 CO2(g) + 8 H2O(l) 0.000488 mole KMnO4 5 mole CaC2O4 1 mole Ca+2 40.1 g Ca+2 1000 mg .00205 L KmnO4 x ---------------------------- x ------------------- x ------------------ x -------------- x ----------- = 0.100 mg Ca+2 1 L KMnO4 2 mole KMnO4 1 mole CaC2O4 1 mole Ca+2 1 g 0.100 mg Ca+2 100 mL x ----------------- = 10.0 mg 1 mL blood • If the 1 mL of blood has a mass of 1.060 g, what is the mass % of the Ca? 0.100 mg Ca+2 % Ca+2 = -------------------- x 100% = 0.00943 % 1060. mg blood

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