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jenicalina

IA Help Please! Iodine Clock

I know when you perform a classic iodine clock reaction, the reacting solution is meant to turn blue-black. 

 

However, when I performed it... not only did it not turn blue black, but instead--- brown?!

 

In my experiment, I added two different solutions:

 

Solution 1 contained:

20mL of a reacting solution (1.5g of KI added to 1.9g of Na2S2O3 in 250cm3 of water)

10mL sulfuric acid (H2SO4)

2mL of dilute starch solution

 

Solution 2 contained:

Distilled water

Variable volumes of hydrogen peroxide (H2O2)

 

Did I do something wrong? I've processed the data that I've collected, and my trends are looking fine, however I just don't know why my solution turned brown-black instead of blue-brown, nevertheless explain this in my conclusion. If it helps, the reaction did smell....

 

Could it be that the reaction that I did wasn't really an iodine clock at all..?

 

 

Any help or suggestions would be greatly appreciated!!

 

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Maybe you didn't have enough starch? That's sort of unlikely but starch does turn completely black/blue in the presence of Iodine. Or possibly, your KI was impure. I can't think of anything else.

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