Hi all. This is my first post on this boards. Happy to be here.
I'm setting up to do an iodine clock reaction, and cannot find liquid starch anywhere in town. (only in aerosol sprays) Reagent grade soluble starch
bought online seems way too expensive, and it seems that it would be simple to make starch cold-water soluble. I've googled for a method without much
success. The one thing that seems promising is this 1928 patent, which involves treatment with hypochlorite:
Would that be a good way to prepare starch for this use? Other processes I found uses Borax, but I wonder if a bit of sodium borate would interfere
with the clock reaction. (maybe no more than some hypochlorite ions) Does anyone have any other suggestions? I don't want to use potato starch
cooked into a goop.
Apparently, if heated in water, the starch granules irreversibly break down and the starch dissolves.
Correct.. but it also thickens... for the clock reaction you want the starch solution to be as aqueous as possible.
[Edited on 11.10.13 by bfesser]Metacelsus - 11-10-2013 at 10:53
What exactly do you mean by "as aqueous as possible"?Rumirunto - 11-10-2013 at 10:55
Full Definition of AQUEOUS
1
a : of, relating to, or resembling water
Meaning: very fluid. Not thick.bfesser - 11-10-2013 at 11:31
That is a colloquial definition of <em>aqueous</em>, not a chemical definition. If you only use a small amount of starch in a large
volume of water, the viscosity will not be a problem.Mailinmypocket - 11-10-2013 at 11:39
For this reaction very little starch is required. You can easily make a "solution" by stirring starch together with cold water to make a paste, and
pouring that into the requisite amount of boiling water. This should make an acceptable substitute for soluble starch.Semmelweis - 11-10-2013 at 11:52
Use corn starch, dissolve one level teaspoon in 400ml or more water, filter two or three times (can be done with coffee filters).
You will get an solution that is sufficiently aqueous, yet readily turns blue in addiction of iodide-iodine, indicating suitability for this clock
reaction.
Keep it simple. To do otherwise you'd need quite high concentrations of hypochlorite. Also, you' d have the problem of removing it from the starch,
otherwise chlorine would be likely liberated when you did the experiment.Mailinmypocket - 11-10-2013 at 12:03
No need to filter or muck around with bleach and stuff. Cold water starch paste, mixed into boiling water works fine. Rumirunto - 11-10-2013 at 12:07
Great.. will try it with plain and simple potato starch. Thanks for the feedback. I'll post how it turned out.
