An alternative titration method for determining the concentration of vitamin C i
ID: 537730 • Letter: A
Question
An alternative titration method for determining the concentration of vitamin C in a sample is to use an iodine solution. In this reaction iodine oxidizes the ascorbic acid to C_6H_6O_6. A 20.00 mL sample of a t 00 mg/mL vitamin C solution is placed in a flask along with 1 ml of a 1 % starch solution to serve as an indicator. A dilute solution of iodine is placed in a buret. A titration is performed using the intense blue color produced y the reaction of excess h with the starch as an indicator that the endpoint has been achieved. The titration was repeated using a 20.00-mL sample of juice. The following data were obtained in this experiment. Determination of Vitamin C Concentration by Redox Titration, Discussion Questions A popular way in chemistry to demonstrate oxidation states changes that occur as chromium is reduced. a. A solution of potassium dichromate is reduced to chromium[III] ions by zinc metal in the presence of an acid causing the solution to change in color from orange to green. What is the oxidation state of the chromium in the potassium dichromate molecule? b. Write the balanced half reactions and net ionic equations for this reaction.Explanation / Answer
2. Vit C by redox reaction with I2
volume of I2 needed for 20 mg Vit C sample = 5.31 ml
For juice sample volume needed = 2.85 ml
Thus,
concentration of ascorbic acid in juice sample = 2.85 x 20/5.31 = 10.734 mg
= 10.734/20 = 0.54 mg/ml
Discussion
1. Oxidation state of Cr in K2Cr2O7 = +6
2. balanced half reactions,
Cr2O7^2- + 14H+ + 6e- ---> 2Cr3+ + 7H2O
Zn ---> Zn2+ + 2e-
Net ionic equation,
Cr2O7^2- + 3Zn + 14H+ ---> 2Cr3+ + 3Zn2+ + 7H2O
c. Balanced half-reactions,
Cr3+ + e- ---> Cr2+
Zn --> Zn2+ + 2e-
net ionic equation,
2Cr3+ + Zn ---> 2Cr2+ + Zn2+
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.