Redox Reaction of Ascorbic Acid using IO3

  1. 1. The problem statement, all variables and given/known data

    Equation 1 - IO3- (aq) + 6 H+ (aq) + 5 I- (aq) -> 3 I2 (aq) + 3 H20

    The iodine formed will react with the ascorbic acid.

    Equation 2 - C6H8O6 + I 2 -> C6H6O6 + 2 I- (aq) + 2 H+ (aq)

    The goal is to determine the ascorbic acid concentration (mg/mL) in a Vitamin C solution. A 10mL sample Vitamin C solution was pipetted into an Erlenmeyer flask, to which water, .5 g KL(s), 5 mL of 1M HCl solution, and 1 mL 1% starch solution was mixed thoroughly.

    Titration began with .0137M KIO3.

    To reach the endpoint indicated by the blue color of the idoine-starch complex, required 18.96 mL IO3- solution.

    2. Relevant equations

    a. calculate the number of moles IO3- required for titration.

    b. Calculate the number of moles of I2 (as I3-) produced in the reaction mixture.

    c. Calculate the number of moles of ascorbic acid (176.14 g/mole) present in the 10-mL alquot. Calculate the molarity (M) of the ascorbic acid solution.

    d. Calculate the mg/mL of ascorbic acid in the solution.

    3. The attempt at a solution

    a. I am assuming the easiest way to find the number of moles I03- required for titration is to take the 18.96 mL, convert it to L and multiply it by Molarity. But the Molarity I have known is for KIO3 (.0137M)

    I didn't want to run this calculation without further clarification as to whether or not this is correct. Thanks!
    Last edited: Sep 29, 2010
  2. jcsd
  3. Borek

    Staff: Mentor

    If I understand you correctly you are not sure if the concentration of IO3- is identical to the concentration of KIO3?
    Last edited by a moderator: Aug 13, 2013
  4. Yes. I am not sure if "a. calculate the number of moles IO3- required for titration."

    Is going to be (18.96 mL IO3- Solution) * (.0137M KIO3 required for titration)
  5. Borek

    Staff: Mentor

    Do you know how KIO3 dissociates?
    Last edited by a moderator: Aug 13, 2013
  6. Borek

    Staff: Mentor

    I guess your book doesn't state anything as it assumes you to know that after earlier examples of different salts - most of them behave exactly the same way, listing each one separately doesn't make sense.

    KIO3 -> K+ + IO3-

    Now, if thats how the salt dissociate, and you are given concentration of KIO3, does it differ from teh concentration of IO3-?
    Last edited by a moderator: Aug 13, 2013
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