CourseCourseConceptConceptDocsDocuments

CAIE A-Level Chemistry A2 26.1.5 Mechanisms and Rate Determining Step Questions

Practise checking mechanisms against a rate equation and overall reaction and identifying intermediates or catalysts.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • sum elementary steps and cancel intermediates or catalysts to recover the overall equation
  • match the molecularity of the slow step, or its derived precursor relation, to the observed rate law
  • identify an intermediate as produced then consumed and a catalyst as consumed then regenerated

CAIE A-Level Chemistry A2 26.1.5 Mechanisms and Rate Determining Step Questions question 1

[Maximum number: 2]

Question (a)

(a)

A four-step mechanism is suggested for the reaction between hydrogen peroxide and iodide ions in an acidic solution.

step 1H2O2+I−→IO−+H2O1 \quad \mathrm{H}_{2} \mathrm{O}_{2}+\mathrm{I}^{-} \rightarrow \mathrm{IO}^{-}+\mathrm{H}_{2} \mathrm{O}

step 2H++IO−→HIO2 \mathrm{H}^{+}+\mathrm{IO}^{-} \rightarrow \mathrm{HIO}

step 3HIO+I−→I2+OH−3 \mathrm{HIO}+\mathrm{I}^{-} \rightarrow \mathrm{I}_{2}+\mathrm{OH}^{-}

step 4OH−+H+→H2O4 \mathrm{OH}^{-}+\mathrm{H}^{+} \rightarrow \mathrm{H}_{2} \mathrm{O}

Step 1 is the rate-determining step.

[ 2 ]

Question (i)

(i)

Use this mechanism to construct a balanced equation for this reaction.

[ 1 ]

Question (ii)

(ii)

Deduce the order of reaction with respect to each of the following.
H2O2=\mathrm{H}_{2} \mathrm{O}_{2}=I−=\mathrm{I}^{-}=

H+=\mathrm{H}^{+}=
[ 1 ]
All question bank results loaded