Chemistry 9701/43 — October/November 2023

Cambridge A-Level · A Level Structured Questions · worked solutions for every part, with the mark scheme

questions

100

marks

120

minutes

Topics Transition Elements · Hydrocarbons · Reaction Kinetics · Introduction to A Level Organic Chemistry · Analytical Techniques · Halogen Compounds · +7 more

Q1Reaction KineticsFree sample

Fluorine reacts with chlorine dioxide, $\text{ClO}_2$ , as shown.

\text{F}_2(\text{g}) + 2\text{ClO}_2(\text{g}) \rightarrow 2\text{FClO}_2(\text{g})

The rate of the reaction is first order with respect to the concentration of $\text{F}_2$ and first order with respect to the concentration of $\text{ClO}_2$ . No catalyst is involved.

(a)

(i)

Suggest a two-step mechanism for this reaction.

step 1 $\rightarrow$

step 2 $\rightarrow$

(ii)

Identify the rate-determining step in this mechanism. Explain your answer.

(b)

When the rate of the reaction is measured in $\text{mol}\,\text{dm}^{-3}\,\text{s}^{-1}$ the numerical value of the rate constant, $k$ , is 1.22 under certain conditions.

(i)

Complete the rate equation for this reaction, stating the overall order of the reaction.

\text{rate} =

overall order of reaction =

(ii)

Use your rate equation in (i) to calculate the rate of the reaction when the concentrations of $\text{F}_2$ and $\text{ClO}_2$ are both $2.00 \times 10^{-3}\,\text{mol}\,\text{dm}^{-3}$ .

\text{rate} = \text{..............................}\,\text{mol}\,\text{dm}^{-3}\,\text{s}^{-1}

(c)

Under different conditions, and in the presence of a large excess of $\text{ClO}_2$ , the rate equation is as shown.

\text{rate} = k_1[\text{F}_2]

The half-life, $t_{\frac{1}{2}}$ , of the concentration of $\text{F}_2$ is $4.00\,\text{s}$ under these conditions.

(i)

Calculate the numerical value of $k_1$ , giving its units.

Give your answer to three significant figures.

k_1 = \text{..............................}\quad \text{units } \text{..............................}

(ii)

An experiment is performed under these conditions in which the starting concentration of $\text{F}_2$ is $0.00200\,\text{mol}\,\text{dm}^{-3}$ .

Draw a graph on the grid in Fig. 1.1 to show how the concentration of $\text{F}_2$ changes over the first $12\,\text{s}$ of the reaction.

Fig. 1.1

(iii)

Use your graph in Fig. 1.1 to find the rate of the reaction when the concentration of $\text{F}_2$ is $0.00100\,\text{mol}\,\text{dm}^{-3}$ . Show your working on the graph.

\text{rate} = \text{..............................}\,\text{mol}\,\text{dm}^{-3}\,\text{s}^{-1}

The rest of this paper

8 more questions

Q2Equilibria14M
Q3Chemical Energetics · Reaction Kinetics · Electrochemistry17M
Q4Transition Elements · Group 27M
Q5Transition Elements12M
Q6Transition Elements6M
Q7Introduction to A Level Organic Chemistry · Hydrocarbons · Analytical Techniques8M
Q8Introduction to A Level Organic Chemistry · Hydrocarbons · Halogen Compounds · Analytical Techniques · Nitrogen Compounds · Hydroxy Compounds14M
Q9Hydrocarbons · Carboxylic Acids and Derivatives · Halogen Compounds13M

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