A-Level AQA Chemistry Physical Chemistry Practicals: A student carried out an experim

Question

A student carried out an experiment to find the temperature rise for a reaction between hydrochloric acid and sodium hydroxide solution.

- The student used a measuring cylinder to place 50 cm³ of 0.400 mol dm⁻³ sodium hydroxide solution into a glass beaker.
- The student recorded the temperature at one-minute intervals for three minutes.
- At the fourth minute the student added 50 cm³ of 0.400 mol dm⁻³ sodium hydroxide solution and started to mix the solutions, but did not record the temperature.
- The student recorded the temperature at one-minute intervals for a further eight minutes.

The results are shown in Table 3.

Table 3

Time / min
0   1   2   3   4   5   6   7   8   9   10   11   12
Temperature / °C
19.8   19.8   19.8   19.8   21.6   21.7   21.5   21.3   21.2   21.1   21.2   21.1   21.1

0 4.1.1 Plot a graph of temperature against time on the grid opposite.
Use your graph to find the temperature rise, ΔT, at the fourth minute.
Show your working on the graph by drawing suitable lines of best fit.

0 4.1.2 The uncertainty in each of the temperature readings from the thermometer used in this experiment was ±0.1 °C.
Calculate the percentage uncertainty in the value for the temperature rise.

Percentage uncertainty ______

0 4.1.3 Suggest a change to the experiment that would minimise heat loss.

0 4.1.4 Suggest and explain another change to the experiment that would decrease the percentage uncertainty in the use of the same thermometer.

0 4.1.5 A second student completed an experiment to determine the enthalpy of neutralisation for the reaction between ethanoic acid solution (HOOC-COOH) and potassium hydroxide solution.

The student added 25 cm³ of 0.80 mol dm⁻³ ethanoic acid solution to 75 cm³ of 0.60 mol dm⁻³ potassium hydroxide solution.
The temperature increased by 3.2 °C.

Give an equation for the reaction between ethanoic acid solution and potassium hydroxide solution.
Calculate the enthalpy change (ΔH) per mole of water formed in this reaction.
Assume that the specific heat capacity of the reaction mixture is 4.2 J·K⁻¹·g⁻¹ and that the density of the reaction mixture is 1.00 g·cm⁻³.

ΔH ______________ kJ mol⁻¹

0 4.1.6 In a similar experiment to that in Question 0 4.5, the enthalpy of neutralisation for the reaction between sulfuric acid and potassium hydroxide solution was found to be -57.0 kJ mol⁻¹ per mole of water formed.
Suggest an explanation for the difference between this value and your answer to Question 0 4.5.
(If you were unable to obtain an answer to Question 0 4.5, you should assume a value of -28.5 kJ mol⁻¹. This is not the correct answer.)

A student carried out an experiment to find the temperature rise for a reaction between hydrochloric acid and sodium hydroxide solution - AQA - A-Level Chemistry - Question 4 - 2018 - Paper 3

Worked Solution & Example Answer:A student carried out an experiment to find the temperature rise for a reaction between hydrochloric acid and sodium hydroxide solution - AQA - A-Level Chemistry - Question 4 - 2018 - Paper 3

0 4.1.1 Plot a graph of temperature against time on the grid opposite.

0 4.1.2 Calculate the percentage uncertainty in the value for the temperature rise.

0 4.1.3 Suggest a change to the experiment that would minimise heat loss.

0 4.1.4 Suggest and explain another change to the experiment that would decrease the percentage uncertainty in the use of the same thermometer.

0 4.1.5 Give an equation for the reaction between ethanoic acid solution and potassium hydroxide solution.

0 4.1.6 Suggest an explanation for the difference between this value and your answer to Question 0 4.5.

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