This experiment is for advanced students.

In gas form, element #59 is deadly. However, when iodine is in liquid form, it helps heal cuts and scrapes. The iodine molecule occurs in pairs, not as a single atom (many halogens do this, and it’s called a diatomic molecule). It’s hard to find iodine in nature, though it’s essential for staying healthy… too little iodine in the body takes a heavy toll on how well the brain operates.

A chunk of iodine is blackish-blue, and will sublimate (go from a solid straight to a gas). Iodine is the heaviest element needed by living things. Iodized salt is sodium chloride fortified with iodine to prevent people from not getting enough iodine in their daily diets.

Iodine is found in seaweed (kelp) and seafood as well as vegetables that are grown in dirt that has high iodine levels. People that live inland and do not eat fish often have lower iodine levels than their coastal, fish-eating neighbors. The trick is not to get too much or too little iodine in your diet, because the symptoms of deficiency and excess levels are quite similar.

Starch (like cornstarch) are used as an indicator for detecting iodine in chemistry experiments. When combined with iodine, starch forms a blue-black color in the solution. We’re going to do this and many other activities in this lab, because this experiment is actually several labs rolled into one. First, we have to make iodine, store it, and then we get to use it in several experiments. Are you ready?

[am4show have=’p8;p9;p11;p38;p92;p52;p91;’ guest_error=’Guest error message’ user_error=’User error message’ ]

Materials:

• Goggles
• Gloves
• Glass jar
• Chemistry stand
• Test tubes
• Test tube holder
• Measuring spoon
• Corn starch peanut
• Water cup
• 90 degree bend glass tubing
• One-hole rubber stopper
• Paper towels
• Stain-free work surface
• Solid rubber stopper
• Denatured alcohol
• Dark brown glass storage bottle for iodine
• Dropper pipettes
• Alcohol burner
• Lighter
• Measuring syringe
• Water
• Potassium iodide KI (MSDS)
• Potassium permanganate KMnO4 (MSDS)
• Sodium hydrogen sulfate NaHSO4 (MSDS) AKA: Sodium Bisulfate Sodium hydrogen sulfate is very toxic. Respect it, handle it carefully and responsibly. Do not take it for granted.

NOTE: Be very careful when handling the sodium hydrogen sulfate – it’s highly corrosive and dangerous when wet. Handle this chemical only with gloves, and be sure to read over the MSDS before using.

Remember that iodine is toxic paper and harmful to the environment.
Safely shake test tube to homogenize chemicals using a solid rubber stopper and dispose of in the outside trash.

NOTE: Heat slowly and carefully. You don’t want your test tube in the flame. The end of the glass tubing should not extend into the alcohol. From time to time, touch the end of the glass tubing to the alcohol to rinse iodine from the tube into the alcohol, but the glass tubing shouldn’t reside in the alcohol. Conduct this experiment outdoors or in an extremely well ventilated area inside the house.

Follow cleanup instructions carefully for safety. These are very toxic substances we are working with.

As heating progresses, purple gas will form in the upper test tube. A brown color will begin to form in the alcohol. Heat until purple smoke disappears from the upper test tube.

C3000: Experiments

Here’s what’s going on in this experiment:

2KI + KMnO₄ + NaSO₄ + H₂O–> I₂ + MnO₂ + KOH +KIO₃ + Na₂SO₄

Potassium iodide and potassium permanganate and sodium sulfate and water are heated to produce free iodine gas and magnesium oxide and potassium hydroxide and potassium iodide and sodium sulfate.

All this to produce the iodine we need for the next several experiments.

Cleanup: We are going to clean everything thoroughly after we finish the lab. After cleaning with soap and water, rinse thoroughly. Chemists use the rule of “three” in cleaning glassware and tools. After washing, chemists rinse out all visible soap and then rinse three times more.

Storage: Place cleaned tools and glassware in their respective storage places.

Disposal: Liquids need to be filtered through a paper towel and washed down the drain with plenty of water. Solids are thrown in the outside trash.

Going Further

*Save all solutions you make in these experiments. You will use them in the other experiments.

Testing Iodine solution

After the drops of iodine are in the test tube with water, observe. Any solid particles in the test tube prove that our iodine is not soluble in water.

Addition with Iodine

Using the solution from the above experiment, adding KI will dissolve all the solids that were observed. Why did the solids disappear? Well, nothing dramatic was seen, but an addition compound was created.

I₂ + KI –> KI I₂

Sodium Thiosulfate

Sodium thiosulfate (Na2S2O3) solution is pipette drop by drop to above solution until it turns clear. The reaction that takes place turns our solution into sodium hypoiodite (NaOI)

Packing Peanut

We fill a glass jar with water and 10 drops of iodine and mix well. The water will be a pale brown. Dissolve a corn starch peanut in water. When we add starch solution to the iodine and water, the water turns clear, then blue. We have just created iodine starch!

Colorless Iodine

Sodium thiosulfate solution from an experiment above. Put a few droppers of this solution into the iodine starch and stir. Colorless! We have a colorless iodine solution….very cool!

Iodine and Heat

To set this one up, dropper one drop of iodine solution into a test tube half-filled with water. Then we regain our bright blue color by adding our starch solution to the iodine water.

When we add heat, The solution turns clear! But, we’re not done. The test tube goes into a half full jar of cool water. The solution in the test tube is turning blue. If you keep doing these actions over and over again, you will keep getting the same results.

Did you notice something? The reaction is ________. Think, now.
(Psst! It’s reversible!)

Colorless Iodine Without Heat

In this experiment we use alcohol to achieve a clear solution. We pour some iodine starch solution into some alcohol and the solution turns clear. The alcohol removed the iodine from the solution.

Click here to download Equilibrium Constants and Reaction Mechanisms.

[/am4show]