prelab

Name: _____________________________

9

Exp 6. Prelab: Analysis of Vitamin C

1. A sample of 0.386 g of Vitamin C (ascorbic acid) was dissolved in enough water to make a 30.0. mL (stock) solution.

[NOTE: Use of chegg.com or other “homework” site to get the answers to these questions is cheating. I wrote this prelab and I do not authorize any person paid by a so-

called educational website to answer these questions for students nor post the answers on the web.] How many mg of Vitamin C are in each mL of

this stock solution?

_______________

2. A 6.00-mL sample of the stock solution in #1 above was used in a titration to standardize a solution of I2(aq). [NOTE: Use

of chegg.com or other “homework” site to get the answers to these questions is cheating. I wrote this prelab and I do not authorize any person paid by a so-called

educational website to answer these questions for students nor post the answers on the web.] The Vitamin C sample required 38.76 mL of the I2(aq)

to reach the endpoint.

(a) How many mg of Vitamin C were in the sample that was titrated? _______________

Hint: Use your answer to #1 above.

(b) How many moles of Vitamin C were in the sample that was titrated? (MM of Vitamin C = 176.1 g/mol)

_______________

(c) How many moles of I2 must have reacted with the Vitamin C in the sample? The balanced equation for the chemical

reaction between Vitamin C (C6H8O6) and I2 is:

C6H8O6(aq) + I2(aq) → C6H6O6(aq) + 2 H+(aq) + 2 I-(aq) _______________

(d) What must be the molarity of the solution of I2(aq) that was used as the titrant? _______________

Hint: Molarity is “moles of solute per liter of solution”. Consider how many mL of this solution were used, and how many moles of I2 were in it!

3. A 90.-mL sample of juice was titrated with the I2(aq) solution described above using a buret. The initial reading of the

buret was 0.24 mL. When the endpoint was reached, the reading on the buret was 33.08 mL. How many mg of

Vitamin C were in the juice sample?

_______________