Edexcel A-Level Chemistry A2 11.6 How to I Obtain Data to Calculate the Order with Respect to the Reactants and the Hydrogen Ion in the Acid Catalysed Questions

Practise Edexcel IAL Chemistry 11.6 by comparing pH and rate data, identifying hydrogen-ion dependence and using the rate equation to select a mechanism.

Exam points

deduce the hydrogen-ion order from controlled pH and rate comparisons
Use rate = k[propanone][H⁺] to identify species required before or in the slow step.

[Maximum number: 1]

Propanone reacts with iodine in both acidic and alkaline conditions.

The rate equation for the reaction between propanone and iodine in acidic conditions is

\text { rate }=\mathrm{k}\left[\mathrm{H}^{+}\right]\left[\mathrm{CH}_{3} \mathrm{COCH}_{3}\right]

The reaction was carried out at two different pH values, all other conditions remaining unchanged.

In the first reaction pH = 2.0
In the second reaction the rate was found to be $\frac{1}{3}$ of the original value.
What was the pH of the second reaction, to 1 decimal place?

0.7

1.5

2.5

2.7

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Edexcel A-Level Chemistry A2 11.6 How to I Obtain Data to Calculate the Order with Respect to the Reactants and the Hydrogen Ion in the Acid Catalysed Questions question 1