Nothing Special   »   [go: up one dir, main page]
Scribd Logo
Upload

Welcome to Scribd!

  • 11 views

    Iodimetric Titration of Vitamin C: Reagents

    Uploaded by

    Ebenezer Effisah
    This document describes an iodimetric titration method to quantify the amount of vitamin C in commercial supplements. The method involves generating iodine triiodide (I3-) from a reaction of iodate and iodide, allowing it to react with ascorbic acid (vitamin C), and then back-titrating the excess I3- with standardized thiosulfate solution. The amount of thiosulfate needed indicates the amount of ascorbic acid present, which can then be used to calculate the milligrams of vitamin C per tablet in commercial supplements. Key steps include standardizing the thiosulfate solution and performing replicate titrations of samples containing dissolved vitamin C tablets to obtain an average

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    Iodimetric Titration of Vitamin C: Reagents

    Uploaded by

    Ebenezer Effisah
    11 views2 pages
    This document describes an iodimetric titration method to quantify the amount of vitamin C in commercial supplements. The method involves generating iodine triiodide (I3-) from a reaction of iodate and iodide, allowing it to react with ascorbic acid (vitamin C), and then back-titrating the excess I3- with standardized thiosulfate solution. The amount of thiosulfate needed indicates the amount of ascorbic acid present, which can then be used to calculate the milligrams of vitamin C per tablet in commercial supplements. Key steps include standardizing the thiosulfate solution and performing replicate titrations of samples containing dissolved vitamin C tablets to obtain an average

    Original Title

    13 (2)

    Copyright

    © © All Rights Reserved

    Available Formats

    PDF, TXT or read online from Scribd

    Did you find this document useful?

    Is this content inappropriate?

    This document describes an iodimetric titration method to quantify the amount of vitamin C in commercial supplements. The method involves generating iodine triiodide (I3-) from a reaction of iodate and iodide, allowing it to react with ascorbic acid (vitamin C), and then back-titrating the excess I3- with standardized thiosulfate solution. The amount of thiosulfate needed indicates the amount of ascorbic acid present, which can then be used to calculate the milligrams of vitamin C per tablet in commercial supplements. Key steps include standardizing the thiosulfate solution and performing replicate titrations of samples containing dissolved vitamin C tablets to obtain an average

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    11 views2 pages

    Iodimetric Titration of Vitamin C: Reagents

    Uploaded by

    Ebenezer Effisah
    This document describes an iodimetric titration method to quantify the amount of vitamin C in commercial supplements. The method involves generating iodine triiodide (I3-) from a reaction of iodate and iodide, allowing it to react with ascorbic acid (vitamin C), and then back-titrating the excess I3- with standardized thiosulfate solution. The amount of thiosulfate needed indicates the amount of ascorbic acid present, which can then be used to calculate the milligrams of vitamin C per tablet in commercial supplements. Key steps include standardizing the thiosulfate solution and performing replicate titrations of samples containing dissolved vitamin C tablets to obtain an average

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    You are on page 1of 2

    13.

    Iodimetric Titration of Vitamin C Exploring Chemical Analysis

    13. Iodimetric Titration of Vitamin C 13

    Ascorbic acid (vitamin C) is a mild reducing agent that reacts rapidly with triiodide (See Section
    16-3 and Box 16-2 in the textbook). In this experiment, we will generate a known excess of I3-
    by the reaction of iodate with iodide (Reaction 16-20), allow the reaction with ascorbic acid to
    proceed, and then back titrate the excess I3- with thiosulfate (Reaction 16-21 and Color Plate 12).

    Reagents

    Starch indicator: Make a paste of 5 g of soluble starch and 5 mg of Hg2I2 in 50 mL of distilled


    water. Pour the paste into 500 mL of boiling distilled water and boil until it is clear.
    Sodium thiosulfate: 9 g Na2S2O3 . 5H2O/student.
    Sodium carbonate: 50 mg Na2CO3/student.
    Potassium iodate: 1 g KIO3/student.
    Potassium iodide: 12 g KI/student.
    0.5 M H2SO4: 30 mL/student.
    Vitamin C: Dietary supplement containing 100 mg of vitamin C per tablet is suitable. Each
    student needs six tablets.
    0.3 M H2SO4: 180 mL/student.

    Preparation and Standardization of Thiosulfate Solution

    1. Prepare starch indicator by making a paste of 5 g of soluble starch and 5 mg of HgI2 in 50


    mL of water. Pour the paste into 500 mL of boiling water and boil until it is clear.
    2. Prepare 0.07 M Na2S2O3 14 by dissolving ~8.7 g of Na2S2O3.5H2O in 500 mL of freshly
    boiled water containing 0.05 g of Na2CO3. Store this solution in a tightly capped amber
    bottle. Prepare ~0.01 M KIO3 by accurately weighing ~1g of solid reagent and dissolving it
    in a 500-mL volumetric flask. From the mass of KIO3 (FM 214.00), compute the molarity of
    the solution.

    13 D. N. Bailey, J. Chem. Ed. 1974, 51, 488.


    14 An alternative to standardizing Na S O solution is to prepare anhydrous primary standard Na S O by
    2 2 3 2 2 3
    .
    refluxing 21 g of Na2S2O3 5H2O with 100 mL of methanol for 20 min. Then filter the anhydrous salt, wash
    with 20 mL of methanol, and dry at 70C for 30 min. [A. A. Woolf, Anal. Chem. 1982, 54, 2134.]

    48
    13. Iodimetric Titration of Vitamin C Exploring Chemical Analysis

    3. Standardize the thiosulfate solution as follows: Pipet 50.00 mL of KIO3 solution into a flask.
    Add 2 g of solid KI and 10 mL of 0.5 M H2SO4. Immediately titrate with thiosulfate until
    the solution has lost almost all its color (pale yellow). Then add 2 mL of starch indicator and
    complete the titration. Repeat the titration with two additional 50.00-mL volumes of KIO3
    solution. From the stoichiometries of Reactions 16-20 and 16-21, compute the average
    molarity of thiosulfate and the relative standard deviation.

    Analysis of Vitamin C

    Commercial vitamin C containing 100 mg per tablet can be used. Perform the following analysis
    three times, and find the mean value (and relative standard deviation) for the number of
    milligrams of vitamin C per tablet.

    1. Dissolve two tablets in 60 mL of 0.3 M H2SO4, using a glass rod to help break the solid.
    (Some solid binding material will not dissolve.)
    2. Add 2 g of solid KI and 50.00 mL of standard KIO3. Then titrate with standard thiosulfate as
    above. Add 2 mL of starch indicator just before the end point.

    49

    You might also like