Electric Rainbow Jelly

[driedle]

My daughter is trying to do this experiment and the directions are horribly lacking in specific details!!!

Materials:
Gelatin
Salt
Buffering agents (sodium bicarbonate? Ammonium chloride + ammonia?)
Universal indicator
Glass or plastic containers
Carbon Rods
Piece of metal
12V or 6 V electric supply
Alligator Clip Test leads

Instructions:

Prepare a strong gelatin solution with gelatin powder from your grocery store. Then dilute it with ten parts water and boil up the Universal Indicator (the BDH brand from Merck & Co works will, but anything a school science lab has will probably work.) This is an alcoholic solution, and adding water and heating it will dilute and evaporate some of the alcohol, which might otherwise stop the gelatin setting. Finally, add the two solutions together and pour into glass or transparent plastic containers. You should balance the amount of indicator added so that the color is not too dark a green. I think the effect is maximized in containers such as flat champagne glasss, which allow you to see the colors developed better. Let the gel set.

Now insert two pieces of carbon rod, one on either side of the gel. Now apply a DC voltage from a battery to the two electrodes in the gel. I used a 12 V car battery, but a 6V battery would work just as well. Gas will be seen bubbling up at both ends at the higher voltages, forming a blob of colored foam around the electrode. There will also be a pungent smell, a strong “essence of swimming pool.” Don’t be tempted to apply the electrolysis current for too long; a couple minutes or so is all that is needed. Now remove the electrodes.

Now wait…wait… and wait. Over the next hours and days, a beautiful rainbow will develop, from red near the positive electrode (anode) to violet near the negative electrode (cathode). If you electrolyzed for too long you will soon have gel with a red side and a violet side and a very thin band of darker colors in a line between them. If you have done it all right, you should have a rainbow of colors forming surfaces arranged concentrically around the spots where the electrodes were. Magically, purple, then blue, then gree, perhaps a hit of yellow, extends from the metal electrode, while a red stain blending to orange extends from the carbon rod.

And Finally , for advanced users:

You will no doubt be able to devise different shapes to put the jelly in before electrolysis: long thin columns, large flat plates. You can also choose different shapes of electrode: perhaps a central carbon rod and a circular surrounding metal electrode.

Try different shapes of electrodes made out of, for example, tin (from cans) or other metals. With these larger electrodes, where do the most intense colors form? Do the edges of the color bands follow lines of equal voltage (equipotentials)?

The colors may be changed, to some extent, by dissolving metal ions. You could use a carbon rod for one electrode if this is troublesome. Iron at the cathode, for example, tends to give a yellow color from the Fe3+ ions there, formed as the iron atoms are ionized.

The use of buffer solutions gives a different background color to the jelly. The addition of small amounts of buffers also has a beneficial influence on the artistic effect because they increase the distance over which the intermediate colors are seen. A typical buffer solution is a salt of a strong acid and a weak alkali with excel alkali, or a weak acid with a strong alkali and excess acid. Examples are respectively ammonium chloride and ammonia mixture or sodium citrate with citric acid. Buffer solutions only slightly change in pH, even with the addition of relatively large amounts of acid or alkali.


My questions are:
1. What do we do with the salt? It is listed in materials, but never mentioned in the instructions.
2. What is a "strong" solution of gelatin?
3. Do we dilute the Universal Indicator with ten parts water??? or dilute the gelatin mixture??
4. Directions and diagram say to place two pieces of carbon rod, one on either side of gel... and makes no mention of the metal in the materials list. Then at the end it says some color will extend from the metal electrode and some from the carbon rod. Are we really supposed to use one carbon rod and one piece of metal. We have a small copper tube, an aluminum tube, and a small plate of brass available to use.
5. Materials list includes buffering agents but they are not mentioned in the main instructions section. Sodium bicarbonate is regular baking soda, correct?? What should we do with it? Do we add it to the solution? How much? When?
6. I am having trouble locating Universal Indicator except online and I think it's too late to order and have in time. Is there anything we can substitute? Any store that might carry???

HELP! I really should have examined this better before I agreed to let her do this one!!!

[deleted-71588]

Is this project from a Neil Downie book?
1) Gelatin has a high resistance and would not produce any chlorine smell so my GUESS is that salt (NaCl) would be added to the gelatin solution to provide an ion path and would be the source of the chlorine gas. BEWARE: Chorine gas is posionous so do in a well vented area.
2) My guess would be a strong solution would be as little water as you can get the gelatin to disolve in since you will be adding solute. You want the final gelatin/indicator/buffer material to set up to a hard rubbery consistency.
3) The instructions aren't clear. The main point is to add water to the indicator and then boil off the alchohol and then mix the strong gelatin with the indicator prep so that you end up with two to three times the amount of gelatin per liquid that the gelatin package calls for so that it will set to a hard rubbery consistency.
4) If you read down in the advanced area it mentions using metalic electrode(s) as a alternative.
5) The advanced section also mentions using buffers as an additional thing to try. It says small amounts, so my guess would be less than 5% of the gelatin powder by weight or volume.
6) Universal Indicator http://en.wikipedia.org/wiki/Universal_indicator is one of the two main ingredients in this project. If you don't have it or can't mix it, then the best you can do is use whatever pH indicator(s) you can find and live with their limited ranges.

This is one of those demonstration projects that maybe fun to do; however, in order to make it into a good Science Fair Project, you need to turn it into a scientific investigation complete with hypothesis and experiment design that will allow you to prove (or disprove) your hypothesis. See the Science Fair Guide https://www.sciencebuddies.org/science- ... ndex.shtml for more information.

[driedle]

Thank you for your help. Yes this is from Neil Downie book!

I spoke with her science teacher and she agreed that we should choose a new topic. She found one that we can do with materials at home and also lends itself better to forming a hypothesis and testing it.