6th edition, 15.87

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Hai-Lin Yeh 1J
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6th edition, 15.87

Postby Hai-Lin Yeh 1J » Thu Mar 14, 2019 10:33 am

The hydrolysis of sucrose (C12H22O11) produces fructose and glucose: C12H22O11(aq) + H2O(l) -> C6H12O6(glucose, aq) + C6H12O6(fructose, aq). Two mechanisms are proposed for this reaction:
(i) Step 1 C12H22O11 -> C6H12O6 + C6H10O5 (slow)
Step 2 C6H10O5 + H2O -> C6H12O6 (fast)
(ii) C12H22O11 + H2O -> C6H12O6 + C6H12O6 (slow)
Under what conditions can these two mechanisms be distinguished by using kinetic data?

Can someone explain this more clearly?

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Re: 6th edition, 15.87

Postby Chem_Mod » Thu Mar 14, 2019 7:52 pm

The premise of this question is to evaluate which mechanism best describes the reaction. Because mechanism I has two steps, we only look at the rate determining step, which is the slow step.

We see that after writing rate laws for mechanism I and II, the only difference is that mechanism II depends on water while mechanism 1 does not. We thus must use experiments to decide whether the reaction mechanism is dependent on water. What we can do is use low sucrose concentration as our control and high concentrations of sucrose for our experiment. We measure how the rate changes over time. In low concentrations of sucrose, the water concentration does not change. In high concentrations of sucrose, the water concentration does change.

Mechanism I is valid if: two experiments show the same kinetics bc it is independent of water
Mechanism II is valid: if the results have different kinetics, indicating that the reaction depends on water

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