MrHomeScientist
International Hazard
Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline
Mood: No Mood
|
|
Iodine Clock Alternatives
I tested out a new demonstration for my science show recently: the classic iodine clock reaction. I start with two beakers of clear liquids and pour
them together. After ~8 seconds, the mixture suddenly and instantly turns black. I then take the black liquid and pour it into another clear liquid,
and the black instantly disappears. It's very striking, highly visible, and perfect for our stage show format.
Unfortunately it also produces sulfur dioxide as a byproduct, which tends to give the presenters nasty sore throats (you might remember I had a
similar problem with another demonstration a few years back - SO<sub>2</sub> returns with a vengeance!). I'm trying to find a substitute
reducing agent for this reaction that will not produce any noxious gases. Any ideas?
For reference here's the procedure I'm following (from http://www.stevespanglerscience.com/lab/experiments/iodine-c... )
| Quote: | Solution A
In 1-Liter of distilled water add 1.2 grams of sodium metabisulfite. Carefully add 4 grams of concentrated sulfuric acid and 10 mL of ethanol.
Solution B
Add 4.3 grams of potassium iodate to 1000 mL of distilled water.
Solution C
Boil water and measure out 50 mL. Add 2 grams of soluble starch and allow to cool.
Presentation Time
In a 250 mL beaker, combine 50 mL of Solution A with 50 mL of distilled water. Now, add 10 mL of Solution C to the mixture.
In a 100 mL beaker, combine 50 mL of Solution B and 50 mL of distilled water.
Get ready to start your stopwatches! Pour the solution in the second beaker into the first beaker. Keep pouring the solutions back and forth into the
beakers for about 8-10 seconds. Watch in amazement as the combined solutions turn an inky black color instantly! Wait for the oohs, ahhs, and applause
from your captivated audience. |
To that I add another beaker with sodium thiosulfate solution, to neutralize the black color and make the final liquid safe for disposal. The
SO<sub>2</sub> comes from Solution A, from acidifying the metabisulfite. Presumably it's this dissolved gas that does the actual reducing
for the reaction to work.
|
|
|
AvBaeyer
National Hazard
Posts: 645
Registered: 25-2-2014
Location: CA
Member Is Offline
Mood: No Mood
|
|
Mr HomeScientist,
I have used the following recipe in the past and it works well. It uses no sulfuric acid.
Solution A: 15 g potassium iodate in 1 liter of solution.
Solution B: 15 g Sodium bisulfite and 2 g soluble starch per liter. Dissolve starch in boiling water, cool, add sodium bisulfite and dilute to 1
liter. This solution deteriorates rapidly and should be prepared fresh as needed.
Iodine clock reaction: Add one (1) volume of Solution A to three (3) volumes of water. Stir vigorously and add one (1) volume of solution B.
This is from JL Lambert and GT Fine, J. Chem Ed. 61, 1037 - 1038 (1984).
Hope this helps,
AvB
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Mine is potassium iodide + H2O2 + sodium thiosulphate + starch.
Peroxide oxidises iodide to iodine, which is reduced back to iodide by thiosulphate, until the latter is used up and iodine causes the starch to go
black. Add it to more thiosulphate to get clear again.
No SO<sub>2</sub> involved whatsoever.
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
Keep the SO2 in the presentation!
Add large gloves, a long stirring rod and a gas mask, of course, due to the SO2 danger!
In other words, introduce some drama to your otherwise 'trying to keep from falling asleep' performance.
Your dialogue could also stress the importance of safety when performing chemical experiments along with some light humor.
What I learned in public speaking is that it is important to capture the audience's attention. Your use (or over use) of safety gear may assist.
In essence, however, not to be publicly admitted to, the safety equipment have become props (not to belittle the actual importance of safety as we are
repeatedly reminded by accidents reported on this forum).
Please note, if your audience/class is normally half asleep, ignore this suggestion and proceed with the advice as provided above.
[Edited on 22-5-2015 by AJKOER]
|
|
|
MrHomeScientist
International Hazard
Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by AJKOER  | | In other words, introduce some drama to your otherwise 'trying to keep from falling asleep' performance. |
Nice of you to judge without ever having seen the performance.
The kids could not be more excited, and "stress[ing] the importance of safety when performing chemical experiments along with some light humor" is
exactly what we do in the show. Perhaps you should learn about the program before commenting?
Thanks blogfast, I'll look into that version. That would be extremely convenient because we already have all those materials on-hand.
A 'clock time' of about 10 seconds is what I'm aiming for.
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by MrHomeScientist |
Thanks blogfast, I'll look into that version. That would be extremely convenient because we already have all those materials on-hand.
A 'clock time' of about 10 seconds is what I'm aiming for. |
There's gotta be a TON of recipes and Utoobs on that method. I did this from a Chemset for my daughter donkeys ago, worked very well.
But she went on to study astrophysics anyway! 
[Edited on 22-5-2015 by blogfast25]
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
