Chemistry 9701/33 — May/June 2013

Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme

questions

marks

120

minutes

Topics Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation · Qualitative Analysis

Q1Manipulation, Measurement and ObservationPresentation of Data and ObservationsAnalysis, Conclusions and EvaluationFree sample

You are to determine the enthalpy change of the reaction between hydrochloric acid and sodium hydroxide by adding various volumes of acid and alkali and measuring the change in temperature.

FA 1 is $0.950\text{ mol dm}^{-3}$ hydrochloric acid, $\text{HCl}$ .
FA 2 is aqueous sodium hydroxide, $\text{NaOH}$ .

(a)

Method

Support the plastic cup in a $250\text{ cm}^3$ beaker.
Using a measuring cylinder, transfer $25\text{ cm}^3$ of FA 1 into the cup and measure the temperature of the acid. Tilt the cup if necessary to cover the bulb of the thermometer.
Record this initial temperature.

$\text{initial temperature of FA 1} = \dots\dots\dots\dots\dots\text{ }^\circ\text{C}$

Use a second measuring cylinder to transfer $10\text{ cm}^3$ of FA 2 and $25\text{ cm}^3$ of water into a $100\text{ cm}^3$ beaker.
Add this mixture to the plastic cup and stir.
Measure the maximum temperature reached and record this maximum temperature in the table below.
Rinse out the plastic cup and shake it to remove excess water.
Repeat the experiment, using the volumes of FA 1, FA 2 and water shown in the table. Record the maximum temperature for each experiment.

volume FA 1 / $\text{cm}^3$	volume FA 2 / $\text{cm}^3$	volume water / $\text{cm}^3$
25	10	25
25	15	20
25	20	15
25	25	10
25	30	5
25	35	0

You are going to plot a graph using these results to find the volume of FA 2 that gives the greatest maximum temperature.

Before you plot the graph, choose two further volumes of FA 2 that will allow you to find more precisely the volume that gives the greatest maximum temperature.

Record the volumes you choose, carry out the experiments and record the corresponding maximum temperatures, in the table.

(b)

(i)

On the grid below, plot the maximum temperature on the $y$ -axis against the volume of FA 2 on the $x$ -axis.

Grid 1

(ii)

Draw two straight lines of best fit on your graph, one to show where the temperature was increasing and the other after the greatest maximum temperature had been reached.

(iii)

Using your graph and the initial temperature recorded in (a), determine the maximum temperature change that could occur when $25\text{ cm}^3$ of FA 1 react with FA 2.

$\text{maximum temperature change} = \dots\dots\dots\dots\dots\text{ }^\circ\text{C}$

(c)

Calculation

(i)

Calculate the energy needed to produce the temperature change in (b)(iii).
(Assume that $4.3\text{ J}$ of heat energy changes the temperature of $1.0\text{ cm}^3$ of solution by $1.0\text{ }^\circ\text{C}$ .)

$\text{energy needed} = \dots\dots\dots\dots\dots\text{ J}$

(ii)

Calculate the number of moles of $\text{HCl}$ used in each experiment.

$\text{moles of HCl} = \dots\dots\dots\dots\dots\text{ mol}$

(iii)

Calculate the enthalpy change, in $\text{kJ mol}^{-1}$ , when $1$ mole of $\text{HCl}$ reacts with $\text{NaOH}$ .

$\text{enthalpy change} = \underset{\text{(sign)}}{\dots\dots} \underset{\text{(value)}}{\dots\dots\dots\dots\dots}\text{ kJ mol}^{-1}$

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2 more questions

Q2Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation15M
Q3Manipulation, Measurement and Observation · Qualitative Analysis15M

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