chemistry

posted by .

Titration of Vitamin C tablets

Prior to titration, Vitamin C samples were dissolved in dilute sulfuric acid, treated with a 60mL portion of 0.3 M KIO3 and excess KI.

Given equations:

(1) ascorbic acid + I2 + 2H2O <--> dehydroascorbic acid + 2I^- + 2H3O^+

(2) IO3^- + 5I^- + 6H3O^+ --> 3I2 + 9H2O

(3)I2 + 2S2O3^2- --> 2I^- + S4O6^2-

To find:

a) Thiosulfate consumed(mmol)
b) Excess I2 (mmol)
c) Ascorbic acid content (mmol)
d) Ascorbic acid conten (mg)


I am unsure how to go about finding these results -- i would think i would use a mol ratio from the given equations, but im confused with what equations to use ... any help would be GREATLY appreciated!

  • chemistry -

    a. Thiosulfate consumed. Remember that molarity = moles/L OR mmoles/mL. So mmoles thiosulfate = M x mL. I assume you have the molarity and the mL of thiosulfate used.

    b. The excess I2 is what was titrated with the thiosulfate in question a. So mmoles I2 = just 1/2 mmoles thiosulfate. You find that from the mole ratio in the I2/S2O3 equation.

    c. How much I2 was present to react with vitamin C? That is 60 mL IO3^- x 0.3 M = 18 mmoles IO3^-. That produced 18 x 6 = 108 mmoles I or 54 mmoles of I2 (equation 2). Now subtract from that the excess I2 present from part b. That will give you the I2 that reacted with vitamin C. And since 1 mole vitamin C is equivalent to 1 mole I2 (equation 1), that will also be the mmoles of vitamin C.
    d.You should be able to convert from mmols to mg.
    Check my thinking.

  • chemistry -

    thank you so much for your help!

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. chemistry

    Ascorbic acid is a weak organic acid also known as vitamin C. A student prepares a 0.20 mol/L aqueous solution of ascorbic acid and measures its pH as 2.40. Based on this evidence, what is the Ka of ascorbic acid?
  2. NEED HELP WITH CHEMISTRY HW

    Ascorbic acid (vitamin C) is a diprotic acid having the formula H2C6H6O6. A sample of a vitamin supplement was analyzed by titrating a 0.2894 g sample dissolved in water with 0.0215 M NaOH. A volume of 10.83 mL of the base was required …
  3. urgent i need help within an hour!

    Ascorbic acid (vitamin C, C6H8O6) is a water-soluble vitamin. A solution containing 83.3 g of ascorbic acid dissolved in 210. g of water has a density of 1.23 g/mL at 55°C Calculate the molarity of ascorbic acid in this solution. …
  4. Chemistry

    Ascorbic acid (vitamin C) is a diprotic acid having the formula H2C6H6O6. A sample of a vitamin supplement was analyzed by titrating a 0.3252 g sample dissolved in water with 0.0284 M NaOH. A volume of 13.27 mL of the base was required …
  5. Chemistry

    Ascorbic acid (vitamin C) is a diprotic acid having the formula H2C6H6O6. A sample of a vitamin supplement was analyzed by titrating a 0.3252 g sample dissolved in water with 0.0284 M NaOH. A volume of 13.27 mL of the base was required …
  6. CHM 300

    How do you find the Mass of Vitamin C in tablet?
  7. Chemistry

    For a tablet containing 500mg vitamin C, Calculate how many mL of 0.095M NaOH are required for titration ( molar mass of ascorbic acid- vitamin c is 1.76.12g/mol) I am not sure of the conversions to use, how to get started with the …
  8. Chemistry

    the titration of an ascorbic acid requires 18.5 mL of .0105 M KIO3. how many mmol of ascorbic acid were in this sample?
  9. Analytical Chemistry

    Could someone show me step by step how to solve this type of problem?
  10. Chemistry

    A student followed the procedure given in the lab exercise to determine the ascorbic acid content in a commercial vitamin C tablet. The students prepared the solution using a 0.460 g vitamin C tablet. The titration required 40.00 mL …

More Similar Questions