Iodine clock reaction for Kaia's birthday party

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Notes on reagents

• KI is allegedly 99.9 percent from China purchased circa 2016-04, seems like it may have picked up some water. Wikipedia MW is 166.028.
• Ascorbic acide/Vitamin C is "Biorigins" brand from Amazon supplier purchased 2016-06. Wikipedia MW is 176.12.
• Peroxide is 30 volumes liquide peroxide for hair bleaching, bought from drugstore circa 2015
• Starch is kitchen cornstarch, probably 1-2 months old.
• H2O is "distilled" water from grocery store (probably really RO deionized), purchased 2016-07-14.

Reagent preparation 2016-07-15

Starch much less than 0.5 percent by weight

Place 1.25 grams dry starch in 250 ml glass reagent bottle. Add approx 280 g distilled H2O. Heat in microwave in 20 second increments to approx. 90C, agitating gently at each step. Leave on hot plate set at 99C (actual temp considerably lower) for approx. 1h, agitating occasionally. Leave overnight to settle, pour off clear liquid.

KI less than 1M

16.02 grams (approx). Dissolve in about 90ml DH2O in 100ml graduated cylinder, stirring with pipette. Wash pipette into cylinder and top up to 100ml. Pour into reagent bottle.

Ascorbic acid 1M

17.61 grams powder. Dissolve in about 90ml DH2O in 100ml graduated cylinder, stirring with pipette. Wash pipette into cylinder and top up to 100ml. Pour into reagent bottle.

Test reactions

Test 1

Cylinder A: Approx 9 ml starch solution, 1 ml peroxide.

Cylinder B: 2 ml KI solution, 1 ml ascorbic acid solution.

No visible change for approx. 2 minutes after mixing. Added additional starch from leftover "sludge"; still no effect. Added approx 2 ml more H2O2 solution; got color change after approx. 15 seconds.

Test 2

Cylinder A: Approx 8 ml starch, 3.2 ml peroxide

Cylinder B: 2 ml KI solution, 1 ml ascorbic acid solution

Color change took about 1 minute 13 seconds. Greenish tinge seemed to indicate uncomplexed iodine

Impressions

Could probably use much less KI and somewhat less vitamin C. During cleanup before prep of test 2, starch solution indicated strongly with a *drop* amounts of I2 solution clinging to the inside of a cylinder I thought I'd washed.

Un-noted tests 2024-02

From memory 2024-03-16:

• Solution A: Approximately 50mL starch cold-dissolved in water, 5mL old “9 percent” peroxide probably from 2016.
• Solution B: Approximately 50mL old KI solution, obviously way too strong. 1g ascorbic acid
• Color change in 1 minute; got an ugly, disappointing dark purplish-brown

More tests 2024-03

0.1M KI used in these tests was prepared using original 2016 KI powder, but dried in a filament dryer for several hours.

Color test around 2024-03-11

• 10 mL of supernatant from starch dissolved cold and left to settle for several days
• 1mL very old “9 percent” H2O2, probably from 2016
• 0.5ml 0.1M KI

Got clear brownish idodine color, but apparent all starch had fallen out; got no color until I dribbled in powdered starch. Then got cloudy purplish blue. Diluted 4:1 and still had plenty of (wrong) color. Over the next few days, starch settled out creating purply-blue glob on the bottom of the tube.

Color test 2024-03-16

Made starch solution 2024-03-13 or 2024-03-14 by boiling an excess of starch in water. Got a “cloudy-frosty” liquid. Allowed to settle until all the cloud was in roughly the bottom 1cm of each of two 1L bottles. Poured off clear supernatant 2024-03-16.

Test solution:

• 10 mL “clear starch” supernatant
• 0.2mL 0.1M KI
• 0.5mL very old “9 percent” H2O2, probably from 2016

Nice clear light-to-medium-blue color

Solution storage/time test 2024-03-16

• Solution A: 200mL “clear starch” supernatant as above, 10mL “old peroxide”, prepared about 12:39ET
• Solution B: 4mL 0.1M KI (possible error, see below), 1.0g ascorbic acid (old, circa 2016?, and probably very wet). H2O to dissolve; 10mL wasn’t enough, another 10mL did it. Started about 12:50ET, finished about 13:00ET.
• Combined at 16:50; capped loosely
• Tightened cap about 16:52
• No color as of 17:50 (clock time); leaving overnight.
• No color in morning
• At about 18:33 after initial mixing, added another 10ml peroxide
• Another 10ml peroxide at about 18:43 after mixing
• Another 10ml at about 18:48 after mixing
• At about 18:55 after mixing, decanted 8ml and added 2ml of 0.1M KI. No obvious effect.
• At somewhere around 18:56, or 18:57, was about to pippette some strong murky leftover starch “dregs” into the decanted solution that had had extra KI added. May have gotten a drop or two into the graduated cylinder… or none. Noticed lower part of solution had changed to very dark, almost opaque blue. Entire solution eventually changed.
• Poured about 10ml (by eye) of original uncolored solution into soda preform. Added 4 drops “murky starch”. No blue color. Presumably the 2ml KI was what changed the previous decanted sample and my noticing it as I was about to drip in starch was coincidental.
• Added original 8ml+2ml solution to 10ml by-eye + drops-of-starch. Blue 8+2 solution was noticeably greenish when poured. Mixture clarified. Went slightly blue at bottom after maybe 15 seconds, reclarified on shaking, developed blue vortex that gradually spread to turn entire combination blue at about 24-25 seconds (counted) after recombination..

2024-03-19

Error test

• Noticed that solution A bottle from 2024-03-16 test was labelled as having 4ml extra peroxide rather than 4ml KI solution. Now unsure what was actually added.
• 2024-03-19 11:47: Added 5ml 0.1M KI to remaining “main body” 2024-03-16 test solution (maybe 220ml to 230ml in bottle after previous test removals.
• Changed to dark blue somewhere around 12 minutes in. No later than 12 minutes 15 seconds.

New test

Made “0.5M” ascorbic acid solution (vitamin is from 2016 and has probably picked up a bunch of water)

• Solution A: 100ml cold “clear starch”, 100 ml H2O deionized, 20ml “old peroxide”
• Solution B: 5ml new 0.5M ascorbic, 5ml 0.1M KI
• Left out for an hour or two to get close to room temperature
• Mixed; solution changed color over several seconds at 36:10 to 36:15 (36 minutes) after mixing
• After around an hour, pipetted in another 1ml of 0.5M ascorbic acid. Solution clarified over about 15 seconds (mostly not agitated because reasons), and went blue again at about 1:50 after addition.

2024-03-20

• Solution A: 100ml cold “clear starch”, 100 ml H2O deionized, 20ml “old peroxide”
• Solution B: 2ml 0.5M ascorbic, 5ml 0.1M KI
• TIme to change: Unknown: well over a couple of minutes, under 50 minute demo lecture time

2024-03-21

Trial 1

• Solution A: 100ml cold “clear starch”, 100 ml H2O deionized, 20ml “old peroxide”
• Solution B: 1ml 0.5M ascorbic, 5ml 0.1M KI
• Solution may have been a bit cold when mixed
• Time to change: 14:50 (changed over 15+ seconds)

Trial 2

Prepared 20ml 0.05M ascorbic acid in two batches, each by diluting 1ml of existing 0.5M stock with deonized water to total volume of 10ml.

• Solution A: 50ml cold “clear starch”, 150 ml H2O deionized, 20ml “old peroxide”
• Solution B: 1ml new 0.05M ascorbic, 10ml 0.1M KI
• Time to change: 1:15. Changed over about 5 seconds. Still very dark blue even with reduced starch.