Chemistry 9701/42 — October/November 2017

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

questions

100

marks

120

minutes

Topics Carboxylic Acids and Derivatives · Electrochemistry · Chemical Energetics · Analytical Techniques · Polymerisation · Hydrocarbons · +7 more

Q1ElectrochemistryReaction KineticsFree sample

The compound chlorine dioxide, $\text{ClO}_2$ , can be prepared by the reaction shown.

\text{NaClO}_2 + \frac{1}{2}\text{Cl}_2 \rightarrow \text{ClO}_2 + \text{NaCl}

(a)

Using oxidation numbers, explain why this reaction is a redox reaction.

(b)

The central atom in the molecule of $\text{ClO}_2$ is chlorine.

Draw the ‘dot-and-cross’ diagram for $\text{ClO}_2$ . Show outer electrons only.

(c)

The reaction between $\text{ClO}_2$ and $\text{F}_2$ is shown.

2\text{ClO}_2 + \text{F}_2 \rightarrow 2\text{ClO}_2\text{F}

The rate of the reaction was measured at various concentrations of the two reactants and the following results were obtained.

experiment	$[\text{ClO}_2]$ / $\text{mol dm}^{-3}$	$[\text{F}_2]$ / $\text{mol dm}^{-3}$	initial rate / $\text{mol dm}^{-3}\text{ s}^{-1}$
1	0.010	0.060	$2.20 \times 10^{-3}$
2	0.025	0.060	to be calculated
3	to be calculated	0.040	$7.04 \times 10^{-3}$

The rate equation is $\text{rate} = k[\text{ClO}_2][\text{F}_2]$ .

(i)

What is meant by the term order of reaction with respect to a particular reagent?

(ii)

Use the results of experiment 1 to calculate the rate constant, $k$ , for this reaction. Include the units of $k$ .

(iii)

Use the data in the table to calculate

(d)

(i)

What is meant by the term rate-determining step?

(ii)

The equation for the reaction between $\text{ClO}_2$ and $\text{F}_2$ is shown.

2\text{ClO}_2 + \text{F}_2 \rightarrow 2\text{ClO}_2\text{F}

\text{rate} = k[\text{ClO}_2][\text{F}_2]

The mechanism for this reaction has two steps.

Suggest equations for the two steps of this mechanism, stating which of the two steps is the rate-determining step.

step 1 ..................................................................................................................

step 2 ..................................................................................................................

rate-determining step = .............................

(e)

By considering the rate equation, explain why the rate increases with increasing temperature.

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7 more questions

Q2Group 2 · Chemical Energetics · Equilibria12M
Q3Nitrogen Compounds · Hydroxy Compounds · Carboxylic Acids and Derivatives · Analytical Techniques · Polymerisation16M
Q4Electrochemistry9M
Q5Chemical Energetics11M
Q6Transition Elements13M
Q7Hydrocarbons · Polymerisation · Introduction to A Level Organic Chemistry · Carboxylic Acids and Derivatives16M
Q8Introduction to A Level Organic Chemistry · Hydrocarbons · Carboxylic Acids and Derivatives · Analytical Techniques10M

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