Measuring Iodine in Water

The recommended daily intake of iodine for a typical adult is about 150μg per day, of which the thyroid gland uses about half. Iodine deficiency results in a condition known as hypothyroidism which produces symptoms such as extreme fatigue, goitre, mental slowing, depression, weight gain, and low basal body temperatures. Excess iodine intake results in symptoms similar to those of iodine deficiency.
Iodine is a known disinfectant and is used to inhibit the growth of microorganisms in the drinking water stored at the International Space Station. Scientists at Iowa State University have developed a simple test to measure the concentration of iodine in this drinking water.

A 10-milliliter water sample is run through a thin, one-centimeter disk that changes colour from white to yellow to orange to rust-red as the concentration of iodine increases. A handheld device, a diffuse reflectance spectrometer, can read the disk's color changes and precisely measure the concentration of molecular iodine, or I₂. The whole process is called colorimetric solid phase extraction.

After a series of successful space tests in 2009 and 2010, this water-testing equipment is now certified operational hardware and is part of the space station's environmental monitoring toolbox.

Reference:
Iowa State University (2011, September 15). Chemists help astronauts make sure their drinking water is clean. ScienceDaily. Retrieved September 20, 2011, from http://www.sciencedaily.com­ /releases/2011/09/110914171753.htm

Further Reading
Mass Conversions
Mole Definitions
Molarity
w/v %
ppm

Suggested Study Questions

1. Convert 150μg to a mass in
   • grams
   • milligrams
   • kilograms
   • nanograms
2. Convert 10 milliliters to a volume in
   • liters
   • microliters
   • nanoliters
   • kiloliters
     
   
   
3. For 150μg of iodine, find the
   
   • moles of molecular iodine
   • moles of iodine atoms
   • number of iodine atoms
   • number of molecules of molecular iodine
     
   
   
4. In the Space Station the iodine is dissolved in the water supply. If an astronaut must consume 3L of water a day in order to consume the recommended daily allowance of iodine, calculate the concentration of the iodine in the water in
   • g/mL
   • ppm
   • M
   • % by mass of iodine
5. Assuming 10mL of the iodine solution from question 4 is run through the water-testing disk as described in the article above. Calculate the mass of iodine present in this sample in
   
   • grams
   • milligrams
   • micrograms
   • nanograms
6. Some water is held in contingency water containers (CWCs) which look like duffle bags and hold about 40kg of water each. Assuming each bag is treated with enough iodine to provide the recommended daily intake of iodine if an adult consumes 3L per day, calculate
   
   • the mass of iodine in each CWC in grams
   • the mass of iodine in each CWC in milligrams
   • the mass of iodine in each CWC in micrograms
     
   • the concentration of iodine in each CWC in g/mL
   • the concentration of iodine in each CWC in ppm
     
   • the concentration of iodine in each CWC in mol/L