lab report

Name: _____________________________

10

Exp 6. Report Form: Analysis of Vitamin C

Raw Data

Vitamin C Stock Solution Preparation:

Mass of Vitamin C (ascorbic acid) used to prepare stock solution _______________

(Total) Volume of Vitamin C stock solution (as prepared; not how much was transferred after!) _______________

Standardization Titrations:

Volume of Vitamin C (ascorbic acid) stock solution used for Titration 1 _______________

Initial iodine(aq) buret Reading, Titration 1 _______________

Final iodine(aq) buret Reading, Titration 1 _______________

Was this titration clearly (or likely) overshot? Y or N

Volume of Vitamin C (ascorbic acid) stock solution used for Titration 2 _______________

Initial iodine(aq) buret Reading, Titration 2 _______________

Final iodine(aq) buret Reading, Titration 2 _______________

Was this titration clearly (or likely) overshot? Y or N

Volume of Vitamin C (ascorbic acid) stock solution used for Titration 3 _______________

Initial iodine(aq) buret Reading, Titration 3 _______________

Final iodine(aq) buret Reading, Titration 3 _______________

Was this titration clearly (or likely) overshot? Y or N

Titrations of Beverage of Choice

Detailed description of beverage of choice: _________________________________________________________

Volume of sample of beverage (For Titration 1) _______________

Initial iodine(aq) buret Reading, Titration 1 _______________

Final iodine(aq) buret Reading, Titration 1 _______________

Was this titration clearly (or likely) overshot? Y or N

Volume of sample of beverage (For Titration 2) _______________

Initial iodine(aq) buret Reading, Titration 2 _______________

Final iodine(aq) buret Reading, Titration 2 _______________

Was this titration clearly (or likely) overshot? Y or N

Volume of sample of beverage (For Titration 3) _______________

Initial iodine(aq) buret Reading, Titration 3 _______________

Final iodine(aq) buret Reading, Titration 3 _______________

Was this titration clearly (or likely) overshot? Y or N

Report Form, Analysis of Vitamin C

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Calculated Quantities and Results, Standardization

# mg per mL of Vitamin C (ascorbic acid) in prepared stock solution: _______________

Titration 1 Titration 2 Titration 3

Mass of ascorbic acid used (mg) _______________ _______________ _______________

Moles of ascorbic acid used _______________ _______________ _______________

Moles I2 used _______________ _______________ _______________

Volume of I2(aq) (titrant) used (mL) _______________ _______________ _______________

Molarity of I2 in titrant solution _______________ _______________ _______________

Average molarity of I2 in titrant solution _______________

Calculated Quantities/Results, Beverage Samples

Titration 1 Titration 2 Titration 3

Volume of I2(aq) (titrant) used (mL) _______________ _______________ _______________

Moles I2 used _______________ _______________ _______________

Moles of ascorbic acid in sample _______________ _______________ _______________

Mass of ascorbic acid in sample (mg) _______________ _______________ _______________

Mass of ascorbic acid per mL of sample (mg/mL)_______________ _______________ _______________

Average Mass of ascorbic acid per mL of sample (mg/mL) _______________

Report Form, Analysis of Vitamin C

12

Analysis

1. What beverage(s) did you analyze? Write down here the serving size (in mL) and the amount of Vitamin C per

serving (in mg) from the label. [NOTE: If the amount of Vitamin C per serving is stated only as a percentage daily allowance (DA), contact your instructor for guidance (you may

need to look up on the web the current value of DA for Vitamin C in the USA)]

2. Using the average value that you determined for the number of mg of Vitamin C per mL of beverage (calculated

from your raw data), along with the volume of one serving size of your beverage (as noted in #1, from the label), calculate

the (experimental) mg of Vitamin C in one serving size of your beverage. How well does your experimental value

agree with the value found on the label? Comment on potential sources of error in the experiment.

3. Comment on the precision of your determinations of both (a) the molarity of the iodine solution (titrant) and (b) the

mg of Vitamin C per mL of beverage. State clearly what you are looking at to assess this.

4. (a) To better quantify the precision comparison noted in #3 above, assume that a rough approximation of the %

uncertainty in each of the determinations can be calculated as follows: First, calculate the range of values (for

both the molarity and the mg/mL quantities) and divide it by 2 (i.e., take the largest value you got in one of your

trials minus the smallest value and divide the result by 2). Then, take that result (for each quantity—molarity and

mg/mL), divide it by the average value of that quantity (calculated on the previous page), and multiply by 100.

Setups/Calcs for % Uncertainty of Molarity of I2 Setups/Calcs for % Uncertainty of mg/mL of Vitamin C in beverage

(b) Based on this measure, which determination was more precise, the molarity of the iodine solution or the mg of

Vitamin C per mL of beverage?