The purpose of this experiment is to prepare crystals of iodine and observe some properties of iodine.
The iodine is prepared by mixing potassium iodide (KI) and manganese (IV) oxide, MnO2 , with phosphoric acid, H3PO4 . The chemical equation for this reaction is
THE PROPERTIES OF IODINE CRYSTALS
1. Scrape a few crystals of iodine (an amount that would form a little pile the size of this “o”) into each of 3 small test tubes. IMPORTANT: DO NOT USE TOO MUCH!
2. Into the first test tube add about 3 cm height of water, stopper and shake the contents for about 15 seconds. Record the colour of the water after shaking and estimate the amount of iodine that has dissolved (for example, very little, about half, most, all).
3. Into the second test tube add about 3 cm height of hexane, stopper and shake the contents for about 15 seconds. Record the colour of the hexane before adding it to the test tube and after shaking with iodine. Estimate the amount of iodine that has dissolved.
4. Take the 3rd test tube to the fume hood, place the tube in a test tube holder, as demonstrated by your teacher, and hold the bottom of the tube at an angle over a flame for about a minute. Be careful not to let the metal test tube holder get in the flame – the heat will melt your latex glove and cause a painful burn. Record your observations.
- 1. In which liquid is iodine more soluble: water or hexane? Explain your answer.
- 2. A student puts a crystal of iodine on a watch glass at room temperature and leaves the watch glass and crystal overnight. The next morning, the crystal has disappeared. Suggest a possible reason why the crystal disappears. (You are entitled to make a guess. No, the crystal is not taken by someone.)
- 3. You have a mixture of sand and iodine. Suggest a way to separate and remove the iodine from the sand. (There is more than one way to do this, so any reasonable method is acceptable. No, you can’t use a pair of tweezers and a microscope because it will take until you are 600 years old to finish the job.)
Summarize the properties and behaviour of iodine. In other words, describe everything you learned about iodine in this experiment?