Discovery Express
  • Welcome!
  • Blog
  • Ask Dr. E!
  • Check out our store!
  • 9 Apples Math Game
  • Your questions answered!
  • Events and Announcements
  • About/Contact

Iodine Clock Reaction

2/16/2018

0 Comments

 
In chemistry, kinetics is the term we use when measuring and studying the rates of reactions. Chemical (or reaction) kinetics involves investigations of how different experimental conditions impact the rate of a chemical reaction. We also use kinetics to make reaction equations that can describe the characteristics of a chemical reaction, such as the physical states of the product(s)!
One classic experiment that showcases two chemical reactions taking place is the iodine clock reaction, discovered by Hans Heinrich Landolt in 1886. He took two colorless solutions and mixed them together. After a little time had passed, the solution suddenly turned dark blue! When he repeated the experiment, he found that the solution turned blue after the same amount of time had passed. Clock reactions (or oscillating reactions) are labeled as such because there is a sudden property change after a predictable amount of time. 
Picture
In this case, the change in property happens to be a colorless solution abruptly becoming a much darker color.


​
Recreate the Experiment at Home!
Picture
Before we get into the reaction equations, it might be easier to see what’s going on instead of trying to imagine it. Luckily, we can recreate this famous experiment with a few items you might have in your medicine cabinet! All of the chemicals you’ll be using are completely safe, but iodine is very good at staining your skin and clothes, so you may want to wear some latex gloves just to be safe. All of the materials can be found in a drugstore or supermarket!


What You’ll Need:

  • Distilled (or tap) water
  • A few disposable cups
  • One 1000 mg vitamin C tablet
  • Tincture of Iodine (2%)
  • Hydrogen peroxide (3%)
  • Liquid laundry starch


First, prepare three solutions: a vitamin C stock, an iodine solution, and a hydrogen peroxide solution. For the vitamin C stock, crush the tablet and dissolve it in 2 oz (59 mL) of water.

The next solution will be one of the reactants. Mix 1 tsp (5 mL) of the vitamin C stock with 1 tsp of iodine and 2 oz of water. Label this as “Solution A”.

To prepare the second reactant, add 2 oz of water to 1 tbsp (15 mL) of hydrogen peroxide and 1/2 tsp (2.5 mL) of liquid starch solution. This will be “Solution B”.

Now you’re ready to begin the reaction! Carefully pour Solution A into Solution B. Then pour the entire solution into the now empty cup. Continue transferring the solution back and forth until you see the color change!


What is Happening?

Because the laundry starch contains sulfuric acid, we created the first reacting solution: hydrogen peroxide with sulfuric acid. Then we added it to a solution containing potassium iodide, sodium thiosulfate, and starch. When these are combined, it creates both the elemental and ion forms of iodine.

First Reaction:
Picture
In this reaction, iodide ions react with hydrogen peroxide to produce elemental iodine, which is blue in the presence of starch. However, before that can happen, the vitamin C quickly reacts and consumes the elemental iodine (that's what is happening in the second reaction below). That’s why we don’t immediately see the change of color!


Second Reaction:
Picture
The second reaction is much quicker than the first, so the reactions can proceed for a short amount of time before the thiosulfate (S4O62-) ion is exhausted in the experiment and the iodine-starch complex’s blue color is visible.
You can repeat this experiment as many times as you’d like! You could even try timing the reaction to see if the blue color appears at the exact same time in each trial.



References:

“Iodine Clock Reaction”. Imagination Station, www.imaginationstationtoledo.org.



Image Credits:

“Iodine Clock”. Released into the public domain under the Creative Commons Attribution-Share Alike 3.0 Unported license. Uploaded on 2/12/18 from commons.wikimedia.org

Hodan, George. “Laboratory Glassware”. Released into the public domain. Uploaded on 2/13/18 from publicdomainpictures.net
0 Comments

Your comment will be posted after it is approved.


Leave a Reply.

    Follow us on Pinterest!
    Picture
    Check out our new game for math education, grades 1-7!

    Archives

    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    March 2017
    February 2017
    January 2017
    December 2016
    November 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015
    August 2015
    July 2015
    June 2015
    May 2015
    April 2015
    March 2015
    February 2015
    January 2015
    November 2014
    October 2014
    September 2014
    August 2014
    July 2014
    June 2014
    May 2014
    April 2014
    March 2014
    February 2014
    January 2014

      Tell us what interests you most, and we'll send you a free PDF of a lesson in that subject!

    Submit

    Categories

    All
    Age 10 12
    Age 12 14
    Age 14 16
    Age 16+
    Age 8 10
    Anatomy/Physiology
    Biology
    Chemistry
    Engineering
    Food Science
    Geology/Earth Science
    Health Science
    Math
    Microbiology
    Physics
    Plant Science
    Psychology
    Weather Science

Proudly powered by Weebly