Iodine Clock Reaction

[remlap12]

Hi all,

I am making Solution A for the Iodine Clock Reaction following this recipe:
0.6g Starch
4.1g Sodium Acetate
30mls Acetic Acid
50g Potassium Iodide
4.7g Sodium Thiosulfate

The solution is very cloudy.
My question is, has anyone made this particular one and if so how long should it take to go clear?
What am I doing wrong?

Thanks in advance!

[linotas]

I did this last week. It worked perfectly. The recipe was slightly different to yours though:

Solution A:
4.1g Sodium Acetate
0.6g soluble starch
50g KI
9.4g sodium thiosulphate
1L water

Solution B:
30ml Glacial acetic acid
500ml 3% H2O2
470ml water

[remlap12]

So linotas, was your solution A clear?
I'm trying another batch but it's not looking good!
My solution B is just 500mls 3% Hydrogen Peroxide and 500mls distilled water

[linotas]

Yes, both solutions were clear. It sounds like the starch isn't dissolving if it is cloudy. Maybe try putting the acid in solution B and see if that works?

[remlap12]

yep will do, thanks!

[mtg]

Wondering if anyone has an update for this reaction.
my old recipe is
1. 0.10M Potassium Iodide (KI 16.60 g/L)
2. 0.01M Sodium Thiosulphate (Na2S2O3.5H2O, 2.48g/L)
3. 3% Starch
4. 0.04M Sodium Persulphate (Na2S2O8. 9.52g/L)
mix 100ml of 1., 10ml of 2., and 1ml of 3.,in a 500ml flask. Add 100ml of 4., and swirl the flask. A blue colour will appear in about 15 seconds. (From Colourful chemistry, John Gipps and Eric Friedman)
As I recall it didn't work that quickly either.

[Marama T]

Here's one that uses H2O2. Using stronger H2O2 results in a faster reaction. https://edu.rsc.org/experiments/iodine- ... 44.article

[LabTechBrooke]

Other than the starch, do the chemicals for this prac keep? I have had a teacher cancel 3 times now.

Solution B - 1% potassium Iodide, 0.2% Sodium thiosulfate, water
Solution C - 10% of 30% H2O2, 1% H2SO4

[Marama T]

I've never had storage issues with those chemicals.

[Mostly_microbes]

I did this last week. It worked perfectly. The recipe was slightly different to yours though:

Solution A:
4.1g Sodium Acetate
0.6g soluble starch
50g KI
9.4g sodium thiosulphate
1L water

Solution B:
30ml Glacial acetic acid
500ml 3% H2O2
470ml water

Reviving this old thread to say that I tried this recipe out today, and can confirm, it works perfectly - 15 second colour change precisely.
My starch solution did not go totally clear, despite my best boiling efforts, but it worked anyway.
My next test will be to see if I can delay the colour change by reducing the amount of KI to get staggered colour changes. Has anyone tried this?

[Marama T]

Wow that's really awesome. Let us know how you go.