Determining Iodide Content of Salt

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Iodine is an element that is critical for normal function of the thyroid gland, which is a key regulator of the body's basic metabolic rate. Iodine is a micronutrient, meaning we require only small amounts of it. For example, adults need about 150 micrograms of iodine in the form of iodide ion per day. However, an insufficient supply of iodide via diet and drinking water causes the non-cancerous enlargement of the thyroid gland known as goiter. Prolonged lack of iodide can lead to loss of thyroid function and the birth defect known as cretinism, which has been recognized since the Middle Ages. Iodide ion, in the form of potassium iodide, may be added to table salt to produce "iodized salt" in order to easily provide the population with a sufficient dietary supply of this essential nutrient. One difficulty with this is that iodide ion is easily oxidized to iodine by atmospheric oxygen" The chemical equation below shows the oxidation of iodide to iodine:

4H+(aq) + 4I−(aq) + O2(g)→ 2I2(aq) + 2H2O(l)
"An accumulation of iodine in a box of table salt would result in the salt's becoming yellow to red in color and the development of a very noticeable bad taste. To avoid this problem, a reducing agent, typically dextrose (C6H12O6) is added to reduce back to colorless iodide any iodine that may be formed" (Wright, 2007). The chemical equation below shows the reduction of iodine to iodide by dextrose:

C6H12O6(aq) + I2(aq) + H2O(l)→ C6H12O7(aq) + 2HI(aq)
In this project, you will test various samples of salt to determine whether they contain this essential micronutrient. In the test, hydrogen peroxide (H2O2) reacts with iodide ion present in the salt sample:

2H+(aq) + 2I−(aq) +H2O2(aq)→ I2(aq) + 2H2O(l)
Starch is also added to the testing mixture, so that any iodine produced will form a blue starch-iodine complex. You will use the colored starch-iodine complex as an indicator, identifying the presence (or absence) of iodine in...
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