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JCE Classroom Activity #92: Testing for Iodide in Table Salt

Tom Kuntzleman's picture
Wed, 11/20/2013 - 20:01 -- Tom Kuntzleman

JCE Classroom Activities are a collection of over 100 chemistry experiments and demonstrations that can be carried out using simple materials found around the house or at grocery store and hardware stores.  For example, JCE Classroom Activity #92 describes how to test for the presence of iodide in iodized salt using only water, iodized salt, 3% hydrogen peroxide, vinegar and liquid laundry starch.  

This activity makes use of the reaction between iodide ion (I-) and hydrogen peroxide (H2O2) in acid to form water and iodine (I2): 

Iodine reacts with starch to form a bluish-black complex:

In JCE Classroom Activity #92, these two reactions are used to test for the presence of iodide ion in iodized salt.  Of course table salt is comprised primarily of sodium chloride (NaCl), but iodized salt has a very small amount (0.006% by mass) of potassium iodide (KI) added.  By adding hydrogen peroxide to a mixture of water, hydrogen peroxide and iodized salt, a color change can be observed due to the formation of the blue-black starch-I2 complex.  If you have some Vitamin C (ascorbic acid) on hand, you can extend this activity.  Ascorbic acid added to the starch-I2 complex will reduce any I2 present in the complex back to iodide ion, causing the black color to disappear:

In the video below, you can check out just how easy it is to pull off this experiment.


If you get a chance, check out some of the other JCE Classroom Activities.  Be sure to let me know if you find an activity that is particularly easy to carry out.  I’m always looking for interesting, yet easy to perform experiments!

Reference: 

Stephen W. Wright, JCE Classroom Activity #92, Testing for Iodide in Table Salt. J. Chem. Educ. 2007, 84, 1616A.

Comments

Deanna Cullen's picture
Submitted by Deanna Cullen on

This can be used in a variety of spots in my curriculum! All of the Classroom Activities can be used within a specific curricular topic, used as an activity just before a holiday, used as review before the exam, used for a ChemClub activity or any number of other ways!

Deanna Cullen

Whitehall High School, MI

@CullenChemEdX 

Submitted by Robert Corcoran on

Nice activity.

I'm curious about your pronounciation of the word "iodine".

When I was at University (a long time ago I should say), the halides were pronounced - floureen, chloreen, bromeen, iodeen.