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Redox Titration

Handout. Redox Titration. Part 1: To determine the percentage of H 2 O 2 in aqueous solution Part 2: To determine the percentage of ascorbic acid in vitamin C. Principles. Concept of redox reaction 2MnO 4 - + 5 H 2 O 2 +6H +  2 Mn 2+ + 5O 2 + 8H 2 O. take 5e - , oxidizer. 0. +7. -1.

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Redox Titration

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  1. Handout Redox Titration • Part 1: To determine the percentage of H2O2 in aqueous solution • Part 2: To determine the percentage of ascorbic acid in vitamin C

  2. Principles Concept of redox reaction 2MnO4- + 5 H2O2 +6H+ 2 Mn2+ + 5O2 + 8H2O take 5e-, oxidizer 0 +7 -1 give 1e-, reducer

  3. Procedures For Part 1 • Rinse the buret with KMnO4, 5 ml each time, three times • Fill the buret with 0.02M KMnO4, record the initial volume in ml • Mass of empty flask ___g

  4. Procedure (Con.) • Mass of flask + 20-22 drops H2O2 __g • Add 75 ml H2O and 10 ml 6 M H2SO4 into the flask • Titrate the H2O2 solution with KMnO4 with constant swirling.

  5. Procedure (Con.) • Endpoint- the pink color persist for at least 30 seconds, record the final volume in ml • Repeat two more times

  6. Procedures for Part 2 • Rinse the buret with I2 solution 3 times, 5 ml each time. • Fill the buret with 0.05M I2 solution record the initial volume in ml • Mass of weighing paper _____g • Pulverize half vitamin C tablet. • Mass of weighing paper + sample__g

  7. Procedure (Con.) • Pour the sample into the flask • Add 75 ml H2O and 5 ml starch indicator • Titrate with I2 solution until the dark blue color persist for 30 or more seconds, record the final volume in ml • Repeat two more times

  8. Reminders • Read the volume from the top of the meniscus • No indicator is needed for part 1 • Put white piece of paper under the flask. • Swirl the flask when you do the titration • Put any unused solutions in waste container on side shelf

  9. Calculations for Part 1 2MnO4-+5 H2O2+2H+ 2Mn2++5O2+8H2O • moles of MnO4- = molarity(0.02M) x volume(ml) 1000(mL/L) • moles of H2O2= moles of MnO4- x 5 2

  10. Calculation(Con.) • gram of H2O2 = moles of H2O2 x 34.01 (MW of H2O2) • % H2O2 = gram of H2O2 x 100% sample mass • sample mass (gram) = weight of (flask + 20-22 drops of H2O2) - weight of flask

  11. Calculations for Part 2 • C6H8O6 + I2  C6H6O6 + 2H+ + 2I- • moles of I2= molarity (0.05M) x volume(mL) 1000(mL/L) • moles of C6H8O6 = moles of I2 • grams of C6H8O6 = moles of C6H8O6 x 176.13 (MW of C6H8O6)

  12. Calculation(Con.) • %C6H8O6 = grams of C6H8O6 x 100% weight of sample • weight of sample (gram) = Wsample+weighing paper - Wweighing paper

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