Rates of reaction

[smeee]

I can't find my "recipe" for the Iodate clock reaction...can anyone help please ?

[ellice]

Hi Smeee,
Just looking quickly, the prac we do uses 0.25M Sodium thiosulfate and 2MHCl, but I am familiar with the Iodate one. Will keep looking at old notes.
Cheers,

[dolphinscales]

i have never done this reaction but i goggled it not sure if that is any help to you but
http://en.wikipedia.org/wiki/Iodine_clock_reaction

good luck finding what you need

[franco]

Hi Smeee,

Following is one I remember doing years ago:

Solution A 4.3g KIO3 per litre
Solution B 0.2g Na2S2O5, 4g soluble starch and 5mL 1M H2SO4 (Na2S2O5 hydrolyzes to NaHSO3 in ionic solution).

Make a paste of the starch in a small amount of water and add to boiling water. Add other chemicals and make up to 1 litre.

If making up solutions more than 24 hours before use, dissolve only the first two chemicals for solution B. The sulfuric acid is added just before use or the concentration of the HSO3- will become too low for a suitable reaction rate.

Hope this helps.

Cheers,
Fran

[smiley]

Hi Smeee,

I use the same recipe as Fran, BUT it is absolutely vital to buy brand new fresh Sodium Metabisulphite for this experiment, to make it work perfectly. I get small amounts from a local brewing shop.

[~megz~]

Hey,

We used the same recipe as Fran's on Friday, and it worked a treat

Good luck!

M

[smeee]

Thank you, thank you, thank you.
It worked even though the chemicals are "old" and probably took a bit longer than if had used newer chemicals.
The chemistry class passed the 2 beakers around to mix solutions and they actually saw the change take place in front of their eyes.
It was "magic"
Thanks again

[lada]

We use different concentration of H2O2 as oxidizing agent in this reaction, and as the conc. decreases, the rate of reaction decreases. If you have a number of groups doing it in the circle, the colour change happens in a clockwise direction.

Reagents
H2SO4 2M
H2O2 20 volume(6%)

starch freshly prepared

reacting solution
1.5g KI added to 1.9g Na2S2O3 in 250ml of water.

Place 20ml of reacting solution to 100ml beaker, then add 10ml 2MH2SO4 and 2 ml starch. Mix well.Decide among the class on conc of H2O2. The volume to be used is 30ml, so make up conc as follows
30ml H2O2
27.5ml H2O2+2.5ml H2O
25ml H2O2 +5ml H2o
22,5ml H2O2+7.5ml H2O
and so on

Place your beaker in a circle and get ready to add your dilution of peroxide, partner to start stop watch as you add the peroxide. The resulting colour is the typical black/blue of iodine and starch.

Good luck.

[smiley]

BTW, did you know you can make a starch solution using the packing worms that are made out of cornstarch? For the clock reaction you use a ratio of 5 "worms" to 100ml of water, or 50 worms for a litre (plus the other stuff - metabisulphite and Acid).

Also good for testing for starch, where you can use one worm per 100mls. Really good in multi-age schools where the labbie does experiment with primary kids.