Battery Blue
Concept: Oxidation and Reduction, Electrolysis, Acids and Base Indicators

Materials:

• 3 beakers
• water
• stirring rod
• 1-9V battery
• 1 gram of Congo red indicator
• Cotton cloth
• spatula
• 2 g potassium iodide
• 10 mL of 3 M sulfuric acid
• 5 mL of starch solution
• spatula spoon or 2 g of ascorbic acid
• 30 mL of 6 M NaOH
• 0.04grams thymolphthalein indicator.
• ethyl alcohol

   

Directions:

Preparing the cloth.

Make a 1% solution of Congo red indicator by adding 1 g of Congo red to 100 mL of distilled or deionized water. Place the cloth in the Congo red solution, immersing it completely. Make sure to wear rubber gloves to protect the skin. Periodically remove the cloth and squeeze out the liquid. Allow the cloth to soak in the liquid for about 15 minutes. Remove the cloth and squeeze out as much liquid as possible then rinse the cloth with fresh water a few times. The red cloth is now ready.

Ptreparing the thymolphthalein solution.

Add 0.04g of thymolphthalein to 50 mL of ethyl alcohol in a beaker. Make up to 100mL with water. If the solutin is coloured add vinegar drop by drop until the solution is clear.

Fill the first beaker with 600 mL of water. This is beaker-1. Add the solid potassium iodide to the beaker and stir until dissolved, and then add 10 mL 3 M sulfuric acid (have 5 mL of starch handy until ready to be put in).

The second beaker should only contain the solid ascorbic acid. This is beaker-2.

Fill the third beaker with 500 mL of water and add 30 mL of 6 M NaOH. This is beaker-3.

When all set up, add starch to beaker-1 and act disappointed as if the experiment did not work.

Drop in the battery.

When the liquid is a black/blue color, pour it in beaker-2. Then soak the cloth in beaker-2, and then in beaker-3.

Beaker 4 contains the thymolphthalein solution prepared earlier.

Introduction:

(Click on the blue writing to show the video)
My favorite color is blue but all I have are these clear solutions. Let us see if I can pour this first chemical in my beaker and make a blue color. Did you see anything? Me neither. How do you think I can make this work? What do you use to make your toys work at home? Everything needs a battery? Can a battery make a chemical reaction? Well let me try this battery. There, I got my blue solution, but how do I get the battery out without getting my hands wet? (Pour beaker-1 into beaker-2)
Well now my blue is gone again. You do not see any blue color? Well, I think the blue color is still there whether you can see it or not. To prove that it is still there I am going to pull the blue color out of the solution. Do you see this red cloth? How about if I dip it into the colorless solution and pull the blue color out of solution on the cloth. See this experiment was successful after all.
Now I want to rinse this cloth so that I can preserve the blue color. (Dip the cloth into beaker-3). Oh, no I lost the blue color again. I guess I will have to give up on the blue color. But I think the blue colour is here somewhere. Let me just squeeze the cloth over the beaker number four.

Explanation:
The first part of the demonstration is in reality an electrolysis reaction with the battery supplying the electrons for the chemical reactions.
These are the electrode reactions:
2H₂O + 2 e^- ====> H₂ + OH^-
At the negative terminal the battery supplies electrons to water to make hydrogen gas. If you look hard enough you can see small bubbles of hydrogen gas forming at the this terminal.

2 I^- ====> I₂ + 2 e^-
At the positive terminal of the battery iodide ions are converted to elemental iodine and gives away two electrons.

The elemental iodine (I₂) reacts with the starch that is present to produce the blue color.
Iodine, I₂ + starch ===> blue-black color

As the blue starch/iodine solution is dumped into the second beaker, which contains ascorbic acid, Vitamin C, another redox reaction occurs to change the iodine element back into colorless iodide ions. Therefore the blue color with the starch disappears.

The second series of reactions are not redox but acid/base. The red cloth is dyed with Congo red acid/base indicator. The original solution contains sulfuric acid which changes the Congo red to a blue color. Finally the third beaker contains sodium hydroxide, a base, which changes the Congo red indicator back to red color.

Safety Precautions:

Gloves and goggles must be worn as sulfuric acid and NaOH are highly corrosive and can cause severe burns. Precautions must be taken when using Congo red as it can stain clothing and skin.

Congo red is a dye, a biological stain, and a pH indicator. It has been used as a direct fabric dye for cotton to produce a bright red fabric. Biologists use Congo red as a general contrast stain for cellulose.
Congo red is also used as a pH indicator. The color transition is between pH 3.0 and 5.0. Below a pH of 3.0 (very acidic solutions),
the indicator is blue. Above pH 5.0, the indicator is red.