A student dissolved 0.5556 g of potassium iodate in 250.0 mL DI water in a volumetric flask. They then used 20.22 mL of sodium thiosulfate solution during a standardization run against a 25.00-mL aliquot of the potassium iodate solution. Next, the student dissolved two vitamin C pills (total mass = 1.3312 g) in a 250.0 mL volumetric flask. They then followed the procedures in this handout to back titrate a 25.00-mL aliquot of solution containing the vitamin C pill, which took 5.52 mL of the thiosulfate solution to reach the endpoint.
Calculate the following:
a. What was the molarity of the iodate solution?
b. What was the molarity of the thiosulfate solution?
c. How many moles of iodate (from 25.00 mL) was transferred to the flask with vitamin C sample?
d. How many moles of triiodide (I3 - ) was initially generated in the flask from the addition of iodate?
e. How many moles of triiodide were consumed by thiosulfate during the back titration, and therefore were in excess after reaction with ascorbic acid?
f. How many moles of triiodide reacted with ascorbic acid? And from this value, how many moles of ascorbic acid were present in each 25.00-mL aliquot of the sample solution?
g. What was the mass of ascorbic acid present in the 25.00-mL aliquot? From this value, what was the mass of ascorbic acid present in the original 250.0-mL stock solution, and then the ascorbic acid pill itself?
h. What was the percent by mass of ascorbic acid in the pill?