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CAIE A-Level Chemistry A2 26.1.2 Rate Equations and Reaction Order Questions

Practise deducing rate equations and reaction orders from initial-rate data, then applying half-life and rate-constant relationships.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • deduce reaction orders by comparing controlled concentration and rate changes
  • construct and use rate equations from initial-rate data
  • apply half-life and rate-constant relationships to reaction kinetics

CAIE A-Level Chemistry A2 26.1.2 Rate Equations and Reaction Order Questions question 1

[Maximum number: 3]

Hypophosphorous acid is an inorganic acid.
The conjugate base of hypophosphorous acid is H2PO2−\mathrm{H}_{2} \mathrm{PO}_{2}^{-}.

Question (a)

(a)

H2PO2−(aq)\mathrm{H}_{2} \mathrm{PO}_{2}^{-}(\mathrm{aq}) reacts with OH−(aq)\mathrm{OH}^{-}(\mathrm{aq}).

H2PO2−(aq)+OH−(aq)→HPO32−(g)+H2( g)\mathrm{H}_{2} \mathrm{PO}_{2}^{-}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \rightarrow \mathrm{HPO}_{3}^{2-}(\mathrm{g})+\mathrm{H}_{2}(\mathrm{~g})

Table 2.1 shows the results of a series of experiments used to investigate the rate of this reaction.

Table 2.1

Table 2.1

[ 3 ]

Question (i)

(i)

The rate equation was found to be:

 rate =k[H2PO2−(aq)][OH−(aq)]2\text { rate }=k\left[\mathrm{H}_{2} \mathrm{PO}_{2}^{-}(\mathrm{aq})\right]\left[\mathrm{OH}^{-}(\mathrm{aq})\right]^{2}

Show that the data in Table 2.1 is consistent with the rate equation.

[ 2 ]

Question (ii)

(ii)

State the units of the rate constant, k, for the reaction.

[ 1 ]
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