Iodometric Titration of Vitamin C in Airborne S O IStSlt ...

[Pages:1]Iodometric Titration of Vitamin C in Airborne

IO3-

S2O3-2

I3- +

I3-

Vit C

Method

Iodometric Titration is a type of volumetric analysis in which iodine is used to indicate the endpoint of an oxidation reduction titration. First the analyte, such as ascorbic acid, reacts completely in a one to one ratio with a known excess of triiodide. The excess triiodide is then back titrated with thiosulfate until the sharp endpoint is reached. The known total moles of thiosulfate is subtracted from the moles of total triiodide initially put in the solution, which then leaves the remainder of triiodide that reacted with the ascorbic acid. Since the triiodide and the ascorbic acid react in a one to one mole ratio, we are then able to determine moles of vitamin C in the solution.

Immune Support Supplement

XXX YYY

Chemistry and Sample

Prep

IO3- + 8I- + 6H+ ? 3I3- + 3H2O This reaction was used to obtain the known amount of excess triiodide (I3-) H2O + C6H8O6 + I3- ? C6H8O7 + 2H+ + 3IThis was the overall reaction that reacted all of the ascorbic acid with the triiodide I3- + 2S2O3-2 ? 3I- + S4O6-2 After the reaction of triiodide and ascorbic acid, the excess triiodide was then back titrated with thiosulfate (S2O32-)

Ascorbic acid (C6H8O6) was the analyte and reducing agent. Triiodide (I3-) was the oxidizing agent. Thiosulfate (S2O3-2) was a reducing agent used as a back titrant.

The Airborne tablet was ground into a fine powder. A precisely weighed amount of the sample was dissolved volumetrically in 0.009315M KIO3 along with KI and H2SO4 to 500 mL.

Data

Samp. Vol .07131M Total vol

thiosulfate(mL) thiosulfate

1 F: 7.85?0.05 7.85?

I: 0.00?0.05 0.07mL

2 F: 15.60?0.05 7.75?

I: 7.85?0.05 0.07mL

3 F: 24.60?0.05 7.80?

I:16.80?0.05 0.07mL

4 F: 34.35?0.05 7.90?

I: 26.45?0.05 0.07mL

Samp. mass sample moles I3-

1

0.8908g

2.799x10-4

? 0.0002g

?2x10-6

2

0.8914g

2.763x10-4

?0.0002g

?2x10-6

3

0.8937g

2.781x10-4

?0.0002g

?2x10-6

4

0.8719g

2.817x10-4

?0.0002g

?2x10-6

Mass KIO3: 0.9967g ? 0.0002g

Mass of Vit C Tablet: 4.4775g ? 0.0002g

Results and

Error Analysis

Samp Avg Molarity moles I3-

S2O3 1 0.07131 ? 2.799x10-4

5x10-4

?3x10-6

2 0.07131 ? 2.763x10-4

5x10-4

?3x10-6

3 0.07131 ? 2.781x10-4

5x10-4

?3x10-6

4 0.07131 ? 2.817x10-4

5x10-4

?3x10-6

Samp mol Vit C g of VitC

1 0.001120 ? 0.1972 ?

3x10-6

5x10-4

2 0.001124 ? 0.1980 ?

3x10-6

5x10-4

3 0.001122 ? 0.1976 ?

3x10-6

5x10-4

4 0.001118 ? 0.1969 ?

3x10-6

5x10-4

Avg mass percent Vit C in

sample: 22.3% ? 0.2%

Average g Vit C/tablet: 0.9967g ? 0.0090g

95% Confidence Interval: 1.00g ? 0.02g

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