OCR B (Salters) F336: Individual investigation Iodine Clock QUESTION!

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username1082804
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#1
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#1
Hello, my teacher told me that I have to include a mechanism in my coursework and I've looked online but I was unable to find a mechanism for the iodine clock (persulfate-iodide reaction). Would anybody help me? Do I need to make up my own mechanism?

Or is this correct as the mechanism:

Reaction 1: S2O82- (aq) + 2I- (aq) >>> 2SO42- (aq) + I2 (aq) (slow, rate determining)
Reaction 2: S2O32- (aq) + I2 (aq) >>> S4O62- (aq) + 2I- (aq) (very fast)
Reaction 3: I2 + Starch >>> Blue-Black Complex
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hj2324
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#2
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#2
(Original post by chococup123)
Hello, my teacher told me that I have to include a mechanism in my coursework and I've looked online but I was unable to find a mechanism for the iodine clock (persulfate-iodide reaction). Would anybody help me? Do I need to make up my own mechanism?

Or is this correct as the mechanism:

Reaction 1: S2O82- (aq) + 2I- (aq) >>> 2SO42- (aq) + I2 (aq) (slow, rate determining)
Reaction 2: S2O32- (aq) + I2 (aq) >>> S4O62- (aq) + 2I- (aq) (very fast)
Reaction 3: I2 + Starch >>> Blue-Black Complex
what orders did you find for the persulfate and the iodide in the rate equation? 1st order for both?
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username1082804
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#3
Report Thread starter 7 years ago
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(Original post by hj2324)
what orders did you find for the persulfate and the iodide in the rate equation? 1st order for both?
Yes I did, did you do the same reaction for your coursework? Conc and temp?
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hj2324
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#4
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Then you need a different mechanism because the one you have given above contains 2 moles of I- in the rate determining step which would make it 2nd order. You need a mechanism with only 1 I- in the rate determining step. You could suggest an intermediate formed between the persulfate and an iodide for the slow step and then the intermediate reacting with a second iodide in a second fast step.
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