In acidic conditions, iodine reacts with propanone in a substitution reaction. The kinetics of the reaction are investigated using a colorimeter. As the $$$\mathrm{I}_{2}$$$ reacts, the yellow/brown colour of the $$$\mathrm{I}_{2}(\mathrm{aq})$$$ fades to colourless, changing the absorbance of the solution. Known concentrations of $$$\mathrm{I}_{2}(\mathrm{aq})$$$ are used to prepare a calibration curve graph and the absorbance is then measured as the reaction proceeds. What is the rate of reaction at 20 s ?

$5 \times 10^{-6} \mathrm{moldm}^{-3} \mathrm{~s}^{-1}$

$1 \times 10^{-5} \mathrm{moldm}^{-3} \mathrm{~s}^{-1}$

$5 \times 10^{-3} \mathrm{moldm}^{-3} \mathrm{~s}^{-1}$

$1 \times 10^{-2} \mathrm{moldm}^{-3} \mathrm{~s}^{-1}$

Chemistry

IGCSE&ALevel

CAIE

Exam No：9701_w24_qp_11 Year：2024 Question No：14

Answer:

Knowledge points:

2.4.1.1 reacting masses (from formulae and equations) including percentage yield calculations

2.4.1.2 volumes of gases (e.g. in the burning of hydrocarbons)

2.4.1.3 volumes and concentrations of solutions

2.4.1.4 limiting reagent and excess reagent (When performing calculations, candidates’ answers should reflect the number of significant figures given or asked for in the question. When rounding up or down, candidates should ensure that significant figures are neither lost unnecessarily nor used beyond what is justified (see also Mathematical requirements section).) deduce stoichiometric relationships from calculations such as those in 2.4.1 (1)–(4)

8.1.1 explain and use the term rate of reaction, frequency of collisions, effective collisions and non-effective collisions

8.1.2 explain qualitatively, in terms of frequency of effective collisions, the effect of concentration and pressure changes on the rate of a reaction

Answer:

Knowledge points:

Solution:

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