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
     
   
   

Invisible Ink

The CIA has declassified a number of documents from the first World War, some detailing the nature of invisible inks used at that time. These documents are available in the Freedom of Information Act Electronic Reading Room at cia.gov

One recipe for invisible ink was as follows
"A solution of nitrate of soda and starch in water may be carried for example in handkerchiefs or starched collars, starched shorts or anything else starched. These things being laid in this solution and then ironed. The article thus treated is later on again put in water and a solution obtained which can be used for invisible writing. The best means for developing are iodate of potassium."

And the recipe for developing the ink using potassium iodate
"Iodate of potassium, 5 grams with 100 grams of water, 2 g of tartaric acid added."

The beauty of this recipe for invisible ink is that the ingredients would be quite readily available to the spy.
Nitrate of soda (sodium nitrate) could be found in lawn fertilizers.
Iodate of potassium (potassium iodate) could be found in disinfectants.

As all science students know,
starch + iodine solution → blue-black iodine-starch complexBut a person carrying around a bottle of iodine solution may have been a bit suspicious during the war.
Potassium iodate can react with tartaric acid in aqueous solution to produce potassium iodide solution. The iodide ions released can react further with the iodate ions to produce aqueous iodine solution (I_2(aq)):
5I^-_(aq) + IO₃^-_(aq) + 6H⁺_(aq) → 3I_2(aq + 3H₂O_(l)


Reference
http://www.washingtonpost.com/world/cia-recipe-for-invisible-ink-among-newly-released-wwi-era-documents/2011/04/19/AFn5Ej7D_story.html
http://foia.cia.gov/CIAsOldest/Secret-writing-document-one.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-two.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-three.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-four.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-five.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-six.pdf

Further Reading
Naming Ionic Compounds
Writing Ionic Formula
Molecular Mass (Formula Weight)
Percentage Composition
Oxidation and Reduction
Oxidation States (numbers)

Study Questions:

1. Write the formula for each of the following
   
   • sodium nitrate
   • potassium iodide
     
   • potassium iodate
2. Calculate the molecular mass (formula weight) for each of the following:
   
   • sodium nitrate
   • potassium iodide
     
   • potassium iodate
3. Calculate the percentage composition of each of the following:
   
   • sodium nitrate
   • potassium iodide
     
   • potassium iodate
4. What is the oxidation state (oxidation number) of iodine in each of the following:
   
   • potassium iodide
     
   • potassium iodate
   • molecular iodine
5. In the reaction between iodide ions and iodate ions, which species are being
   • oxidized
   • reduced
6. Write half-reaction equations for each of the reactions below:
   
   • iodide → iodine
   • acidified iodate → iodine

Fukushima Radiochemistry

On the 11^th March 2011 at 14:46 Japan Standard Time, a category 9 earthquake was recorded off the northeast coast of Japan. The epicenter was approximately 72 kilometers east of the Oshika Peninsula of Tohoku. The earthquake moved Honshu 2.4 m east and shifted the Earth on its axis by almost 10 cm. The earthquake was recorded as an upper 6 at the prefecture of Fukushima.

6 separate boiling water nuclear reactors make up the Fukushima I power plant. Nuclear reactors numbers 4, 5 and 6 had already been shut down prior to the earthquake for routine maintenance. Nuclear reactors 1, 2 and 3 were shut down after the earthquake but the subsequent tsunami flooded the plant and incapacitated the emergency generators which ran the pumps to cool the reactors. Reactors 1, 2 and 3 suffered partial nuclear meltdowns (melting of the core of the nuclear reactor), hydrogen explosions destroyed parts of the buildings housing reactors 1 and 3, an explosion damaged reactor 2's containment which is designed to prevent the release of radioactivity into the environment, and several fires broke out in reactor 4. As the water levels in spent fuel pools dropped, the spent fuel rods began to overheat.
On 25th March, Japan's nuclear regulator announced a likely breach of Number 3's containment vessel. World wide measurements of wind-born radioactive iodine and caesium vented from reactors suggested a massive increase in these substances which led to bans on the sale of food grown within a 100km radius of the Fukushima I plant

Cesium-137 is a radioactive isotope of cesium that is formed during the nuclear fission of uranium. It has a half-life of 30.17 years and decays by beta emission to metastable barium-137. Cesium-137 is soluble in water, and its behaviour in living things is similar to that of potassium. The biological half-life of cesium is about 70 days. Experiments with dogs have shown that a dose of 44μg/kg of cesium-137 is lethal within 3 weeks. Prussian blue, Fe₇(CN)₁₈.14H₂O, chemically binds cesium-137 and speeds up its expulsion from the body, so it can be used to treat ingestion of cesium-137.

Iodine-131, also called radioiodine, makes up about 3% of the products of uranium fission. It undergoes beta decay and has a half-life of about 8.02 days. High doses of iodine-131 can be less dangerous than low doses since high doses tend to kill thyroid tissues which could otherwise become cancerous as a result of the radiation. Ingestion of iodine-131 is treated by taking iodine supplements containing non-radioactive iodine-127 as iodide ions. This raises the total amount of iodine in the body and therefore reduce the uptake and retention of radioactive iodine-131.

Reference:
http://www.newsdaily.com/stories/tre72l501-us-japan-contaminants/

Further Reading:
Isotopes
Nuclear Decay
Half-life

Study Questions:

1. Explain what is meant by the term nuclear fission.
2. Give the atomic number and mass number for each of the following:
   
   • uranium-235
   • uranium-238
   • cesium-137
   • iodine-131
3. How many protons and neutrons are contained within the nucleus of each of these atoms:
   
   • uranium-235
   • uranium-238
   • cesium-137
   • iodine-131
4. Explain what is meant by beta decay.
5. Write balanced chemical equations for the beta decay of each of the following:
   
   • cesium-137
   • iodine-131
6. What does a Chemist mean by the term half-life?
7. If a 20kg dog ingests 880μg of cesium-137, how much cesium-137 will remain after 3 weeks? (The half-life of cesium-137 is about 30.17 years)
8. "The biological half-life of cesium is about 70 days". What do you think this means?
9. If a 20kg dog ingests 880μg of cesium-137, how much cesium-137 will remain in the dog's body after 70 days?
10. Iodine pills were distributed to people living around the Fukushima power plants on 12^th March. A typical emergency dose is 130 milligrams of potassium iodide. What mass of iodine is contained in each dose?
11. The iodine dose contained in the emergency pills is about 700 times larger than the normal nutritional daily need of an adult. What is the approximate mass of iodine is required per adult daily?