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Mix equal volumes of A and B by pouring

back and forth into beakers three times. The

reaction starts on the lst pour and ENDs when

the solution turns black….therefore the name

CLOCK REACTION…it tells you how long

the reaction takes from start to finish!

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What would happenif we did the samereaction but didn’t use any starch. Starchturns iodine black.

1. What about iodine…what does it look like?What if you dissolve some in water?

2. Where can you get starch?

3. What happens when iodine comes in contactwith starch?

Know what do you expect to happen IF the two solutions A and B in the clock reaction don’thave any starch in them?1. Will a reaction still happen?2. Will the result be black?3. What will the result look like?

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What would happen to the timefor the reaction ifwe diluted one of the reactants?

What would happen to the timefor the reaction ifwe heated one orboth solutions?

Solutions for the iodine clock reaction:A. 4.3 g KIO3 per literB. 0.2 g Na2S2O3, 4 g soluble starch and 5 ml concentrated sulfuric acid.

You can slow the reaction down by diluting A and speed it up by adding more sulfuric acid to B.

You can use cornstarch, put 1 tsp in 200 ml waterand heat to boil in microwave….let cool and addto B. You can use a big pinch of A, small pinch of Bthrow in a little sulfuric acid in B and some starch. Then adjust to suit you….

The Reaction

1 2 3 4 Mix Any HSO4- left?

yes

no

1. IO3- + 3HS03- I- +3SO4-2 + 3H+

2.

5 I- + 6H++IO3- 3 I2 (aq) + 3H20 3. I2 +HSO3- + H2O 2I- + SO4-2 + 3 H+

4. I2 + starch == blue solutionI2 solution appears yellowish without starch.

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