6.1 Advanced Physical Chemistry Core Practicals | Edexcel International A Level Chemistry Topic Questions 2017

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1a1 mark

A student investigated the kinetics of the reaction between bromide ions, Br^– , and bromate(V) ions, ${BrO}_{3}^{-}$ , in aqueous acid.

5Br^–(aq) + Br $O_{3}^{-}$ (aq) + 6H⁺(aq) → 3Br₂(aq) + 3H₂O(l)

To determine the rate equation for the reaction, the student varied the concentration of bromide ions, bromate(V) ions and acid in turn.

The effect of the concentration of bromide ions was investigated first.

Procedure

Step 1	Add 10.0 cm³of 0.0050 mol dm^–3 potassium bromate(V), 15.0 cm³of acidified methyl orange indicator solution and 5.0 cm³of 0.00010 mol dm^–3 aqueous phenol to a beaker labelled P.
Step 2	Prepare the contents of beaker Q for Run 1 as specified in the table.
Step 3	Pour the contents of beaker Q into beaker P and start a timer. Pour the contents of beaker P back into beaker Q and place beaker Q on a white tile.
Step 4	Stop the timer as soon as the mixture turns colourless. Record the time, along with the temperature of the solution.
Step 5	Repeat Steps 1 to 4 for the remaining runs.

Contents of beaker Q
Run	Volume of 0.01 mol dm^–3 KBr / cm³	Volume of H₂O / cm³
1	10.0	0
2	8.0	2.0
3	6.0	4.0
4	5.0	5.0
5	4.0	6.0
6	3.0	7.0

Give one reason why the contents of beaker P are poured back into beaker Q in Step 3.

How did you do?

1b4 marks

Methyl orange indicator is bleached colourless by bromine.
Under the experimental conditions, the reciprocal of the time taken for the methyl orange to be bleached (1/t) is proportional to the initial rate.

Explain why phenol is added to the reaction mixture.

(2)

ii)

Give the colour of the reaction mixture before it turns colourless.

(1)

iii)

Give the reason why the temperature is measured in Step 4.

(1)

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1c6 marks

The student’s results are shown.

Volume of KBr / cm³	10.0	8.0	6.0	5.0	4.0	3.0
Time, t / s	23	24	32	39	48	64
(1/t) / s^–1	0.043	0.042	0.031	0.026
Temperature / °C	18	22	22	22	22	22

Complete the table by calculating the remaining values of 1/t.

(1)

ii)

Plot a graph of 1/t against the volume of KBr. Include a line of best fit.

(3)

iii)

State why the volume of KBr is proportional to the concentration of bromide ions in the reaction mixture.

(1)

iv)

State the order of reaction with respect to bromide ions, using your graph.

(1)

How did you do?

1d1 mark

After investigating the effect on the rate of the concentration of bromate(V) ions and the concentration of hydrogen ions, the student obtained the graphs shown.

q3d-paper-6-jan-2022-edexcel-ial-chemistry Deduce the rate equation for the reaction, using these data and your answer to (c)(iv).

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2a1 mark

A student carried out an experiment to determine the enthalpy change when solid lithium chloride, LiCl, dissolved in water to form a solution.

Procedure
Step 1 Use a pipette to place 25.0 cm³ of distilled water into a polystyrene cup.
Step 2 Measure and record the initial temperature of the water.
Step 3 Add 2.12 g of lithium chloride to the water.
Step 4 Stir the mixture and record the highest temperature reached.

Give a reason why a polystyrene cup was used instead of a glass beaker in Step 1.

How did you do?

3 marks

The temperature rise was 12.5°C.

Calculate the enthalpy change for the formation of this solution of lithium chloride.
Include a sign and units in your answer.

[Assume: specific heat capacity of the solution = 4.18 J g⁻¹ °C⁻¹
density of the solution = 1.00 g cm^–3]

How did you do?

1 mark

The thermometer used to measure the temperature change had an uncertainty of ±0.25 °C for each measurement.

Calculate the percentage uncertainty in the temperature change in this experiment.

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2d5 marks

The temperature rise in this experiment was lower than expected, due to heat loss to the surroundings.

Describe changes to the procedure that would give a more accurate temperature rise.

Include the use of a stopwatch and details of a graph you would plot.

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Advanced Physical Chemistry Core Practicals (Edexcel International A Level Chemistry)

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