ASCORBIC ACID REDOX TITRATION LAB REPORT

CHM 3120L
ANALYTICAL CHEMISTRY I
LABORATORY REPORT

EXPERIMENT: DETERMINATION OF ASCORBIC ACID BY REDOX TITRATION
Name:
Section:
Date Experiment Completed:

2.0008 g KIO3 x (1 mol/214 g KIO3) = 0.0093495327 mol KIO3
0.0093495327 mol KIO3 / 0.500 L = 0.0186990654 M KIO3

6 Na2S2O3 + KIO3 + 6 H+ → I-+ 3 H2O + 3 S4O62- + K+ + 12 Na+

0.0187 M KIO3 × 0.025 L = 4.675 x 10-4 mol KIO3
4.675 x 10-4 mol KIO3 x (6 mol Na2S2O3 / 1 mol KIO3) = 0.002805 mol Na2S2O3
0.002805 mol Na2S2O3 / 0.03005 L Na2S2O3 = 0.093344426 M Na2S2O3

Determination of the Ascorbic Acid
Titration
Mass of the ascorbic acid sample, g
Volume of Sodium Thiosulfate solution, mL
Weight % of the Ascorbic Acid in the tablet
1
0.1018
19.50
85 %
2
0.1016
19.20
88 %
3
0.1003
19.20
89 %

IO3- + 8 I- + 6 H+ → 3 I3- + 3 H2O
I3- + 2 S2O32- → 3 I- + S4O62-
C6H8O6 + I3- + H2O → C6H6O6 + 3 I- + 2 H+

TITRATION 1 CALCULATIONS:

Initial mol of I3-
3 x (25 mL / 1000) x 0.0187 M KIO3 = 0.0014025 mol I3-
Mol of I3- remaining after reaction with Ascorbic Acid
(1/2) x (19.50 mL / 1000) x 0.0933 M Na2S2O3 = 9.09675 x 10-4 mol I3- remaining
Mol of Ascorbic Acid = mol of I3- reacted
Initial – Remaining = 4.92825 x 10-4
Mass of ascorbic acid = 4.92825 x 10-4 x 176.12 g = .086796339 g = 86.80 mg
Weight % of ascorbic acid = (mass of ascorbic acid / mass of sample) x 100 = (86.80 mg / 101.8 mg) x 100 % = 85 %

Report you final result:
Weight Percent = 87 % (average)
Uncertainty =