Chemistry 5070/31 — October/November 2023

Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme

questions

marks

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Topics Experimental Contexts · Analysis, Conclusions and Evaluation · Observations and Measurements · Use of Techniques, Apparatus and Materials · Qualitative Analysis · Planning Experiments and Investigations

Q117MObservations and MeasurementsExperimental ContextsAnalysis, Conclusions and EvaluationUse of Techniques, Apparatus and MaterialsFree sample

Hydrochloric acid, $\text{HCl}$ , is neutralised when it is added to aqueous potassium hydroxide, $\text{KOH}$ .

$\text{KOH} + \text{HCl} \rightarrow \text{KCl} + \text{H}_2\text{O}$

The reaction is exothermic.

P is aqueous potassium hydroxide.
Q is $2.24\text{ mol / dm}^3$ hydrochloric acid.

Read all the instructions carefully before starting the experiments.

Instructions

You are going to do six experiments.

(a)

Experiment 1

Rinse and fill a burette with Q.
Place the plastic cup into a beaker.
Use a volumetric pipette to add $25.0\text{ cm}^3$ of P to the plastic cup.
Use a measuring cylinder to add $20\text{ cm}^3$ of water to the plastic cup.
Stir the mixture in the cup with the thermometer and measure its temperature to the nearest $0.5\,^\circ\text{C}$ .
Record this initial temperature in column E of Table 1.1.
Use the burette to add $5.0\text{ cm}^3$ of Q to the plastic cup whilst stirring.
Measure the highest temperature reached.
Record this value in column F of Table 1.1.
Empty the plastic cup and rinse it with water.

Experiments 2–6

Repeat Experiment 1 using the volumes of water and Q shown in columns C and D of the table. Refill the burette as necessary.
Calculate the temperature rise for each of Experiments 1–6 and record them in column G of Table 1.1.

Table 1.1

A	B	C	D	E	F	G
experiment number	volume of P / $\text{cm}^3$	volume of water / $\text{cm}^3$	volume of Q / $\text{cm}^3$	initial temperature of mixture / $^\circ\text{C}$	highest temperature reached / $^\circ\text{C}$	temperature rise / $^\circ\text{C}$
1	25.0	20	5.0
2	25.0	15	10.0
3	25.0	10	15.0
4	25.0	7	18.0
5	25.0	5	20.0
6	25.0	0	25.0

(b)

Draw a graph of temperature rise against volume of Q on the grid in Fig. 1.1.

You should:

plot the point (0,0) as there is no temperature rise when no Q is added
plot temperature rise (column G) against volume of Q (column D) from Experiments 1–6
draw a straight line of best fit for the first three points
draw a straight line of best fit for the last four points
extend the lines so that they intersect.

Fig. 1.1

(c)

The point where the two lines intersect indicates the volume of Q that exactly neutralises $25.0\text{ cm}^3$ of P.

Determine the volume of Q where the two lines on the graph intersect.

volume of Q = ______ $\text{cm}^3$

(d)

Q is $2.24\text{ mol / dm}^3$ hydrochloric acid.

Use your answer to (c) to calculate the concentration of potassium hydroxide in P.

$\text{KOH} + \text{HCl} \rightarrow \text{KCl} + \text{H}_2\text{O}$

concentration of potassium hydroxide in P = ______ $\text{mol / dm}^3$

(e)

State and explain why a plastic cup rather than a metal cup is used in these experiments.

______

(f)

A measuring cylinder is used to measure the volumes of water.

Suggest why the volumes of water in Table 1.1 are not given to one decimal place.

______

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2 more questions

Q2Qualitative Analysis · Experimental Contexts · Analysis, Conclusions and Evaluation17M
Q3Planning Experiments and Investigations · Experimental Contexts6M

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