AQA GCSE Chemistry Chemistry Paper 1 (Higher), 2023: Question 2

11 marks · Standard Demand difficulty · Short Answer

Analyze an investigation into the temperature change of ammonium nitrate dissolving in water, including identifying variables, plotting data, extrapolating a line of best fit, explaining endothermic observations, interpreting uncertainty, and identifying error types.

Practise this question

Question

A multi-part chemistry exam question about an investigation into the temperature change of ammonium nitrate dissolving in water. It includes a method description, a table of results (Table 2), a blank grid for plotting a graph (Figure 2), a second table of repeated results (Table 3), and several sub-questions (02.1 to 02.6) requiring identification of variables, graph plotting, data extrapolation, explanation of endothermic processes, interpretation of uncertainty, and identification of experimental error.
Question text

02 This question is about temperature changes.

A student investigated the change in temperature of a solution when different masses

of ammonium nitrate were dissolved in water.

This is the method used.

1. Measure 200 cm3 of water into a polystyrene cup.

2. Measure the temperature of the water.

3. Add 4.0 g of ammonium nitrate to the water.

4. Stir the solution until all the ammonium nitrate has dissolved.

5. Measure the lowest temperature reached by the solution.

6. Repeat steps 1 to 5 with different masses of ammonium nitrate.

02.1 Give the independent variable and the dependent variable in the investigation.

[2 marks]

Independent variable

Dependent variable

Table 2 shows the results.

Table 2

Mass of ammonium nitrate Lowest temperature of solution

added in grams in ºC

4.0 18.2

8.0 16.2

12.0 15.2

16.0 13.6

20.0 12.4

24.0 7 10.6

02.2 Plot the data from Table 2 on Figure 2.

Draw a line of best fit.

*06* [3 marks]

Figure 2

02.3 Determine the initial temperature of the water.

You should extend your line of best fit on Figure 2.

[2 marks]

Initial temperature of the water = °C

02.4 How do the results show that dissolving ammonium nitrate in water is endothermic?

[1 mark]

The student repeated the experiment three more times.

Table 3 shows the results for 8.0 g of ammonium nitrate.

Table 3

Trial 1 Trial 2 Trial 3 Trial 4 Mean

Lowest temperature

16.2 16.6 16.8 16.4 16.5

of solution in ºC

02.5 The student recorded the mean lowest temperature of the solution for 8.0 g of

ammonium nitrate as 16.5 ± 0.3 ºC.

Explain why the student included ± 0.3 ºC after the mean lowest temperature.

[2 marks]

02.6 What type of error is shown by the results in Table 3?

[1 mark]

Tick ( ) one box.

Random error

Systematic error

Zero error

Mark scheme

Show the mark scheme The mark scheme for Question 2, detailing the expected answers for parts 02.1 through 02.6. It provides the correct independent and dependent variables, plotting criteria, extrapolation instructions, the definition of endothermic, the explanation of uncertainty as a range, and the identification of random error, along with the corresponding marks and specification references.

AO /

Question Answers Extra information Mark

Spec. Ref.

02.1 (independent variable) AO1

mass (of ammonium nitrate) 1 4.5.1.1

RPA4

(dependent variable)

(lowest) temperature (reached allow change in temperature (of 1

by solution) solution)

AO /

Spec. Ref.

02.2 all 6 points plotted correctly allow a tolerance of ± ½ a small 2 AO2

square

allow 1 mark for 4 or 5 points

plotted correctly

AO3

line of best fit 1

4.5.1.1

RPA4

AO /

Spec. Ref.

02.3 line extrapolated to y-axis 1 AO3

(initial temperature)

value for temperature where allow a tolerance of ± ½ a small 1

AO2

extrapolated line meets y-axis square

4.5.1.1

RPA4

AO /

Spec. Ref.

02.4 temperature decreased ignore correct references to 1 AO1

energy transfer 4.5.1.1

– HEMISTRY – – RPA4

AO /

Spec. Ref.

02.5 (0.3 °C) is the uncertainty 1 AO2 9

4.3.1.4

(because 0.3 °C) is the range allow values are (a maximum of) 1 4.5.1.1

about the mean value 0.3 (°C) either side of the mean RPA4

allow (because)

16.8 = 16.5 + 0.3

and

16.2 = 16.5 – 0.3

AO /

Spec. Ref.

02.6 random error 1 AO3

4.5.1.1

RPA4

– HEMISTRY – –

Total Question 2 11

Question 3

How to answer it

Investigating Temperature Changes

What this question tests

This question focuses on Required Practical 4 (RPA4): investigating variables that affect temperature changes in reacting circuits. It assesses your ability to identify variables, plot and interpret graphs (including extrapolation), understand endothermic energy changes, and calculate uncertainty.

Part (a) - Identifying Variables

Question 02.1

💡 Key Knowledge

  • Independent Variable: The thing you change (the "cause").
  • Dependent Variable: The thing you measure (the "effect").

✅ Correct Answers

  • Independent: Mass (of ammonium nitrate)
  • Dependent: (Lowest) temperature reached
2 Marks

🧠 Exam Technique

Look at the table headings. Usually, the first column is the independent variable and the second column is the dependent variable. Always include the unit if it's part of the name, though "mass" alone is enough here.

Part (b) - Graphing & Extrapolation

Questions 02.2 & 02.3

🧠 Plotting the Graph

For 02.2, you must plot all 6 points from Table 2. Use a sharp pencil and a small 'x'. The line of best fit should be a single, straight, continuous line drawn with a ruler that passes through or near all points.

📐 Calculation: Finding the Intercept

02.3 asks for the initial temperature. This is the temperature when 0g of salt was added.

  1. Use a ruler to extend your line of best fit backwards until it hits the vertical (y) axis.
  2. Read the value where the line crosses the axis.
  3. Based on the data (dropping 2.0°C for every 4g), the intercept should be 20.2°C.
2 Marks (1 for line, 1 for value)

❌ Common Errors

  • Drawing a "dot-to-dot" line instead of a line of best fit.
  • Stopping the line at the first data point (4.0g) instead of extending it to the y-axis.
  • Misreading the scale: each small square on the y-axis represents 0.2°C.

Part (c) - Energy Changes

Question 02.4

✅ Correct Answer

The temperature decreased (or went down).

1 Mark

💡 Key Knowledge

In an endothermic reaction, energy is taken in from the surroundings. This causes the temperature of the surroundings (the solution) to drop. If the temperature had increased, it would be exothermic.

Part (d) - Uncertainty & Error

Questions 02.5 & 02.6

🧠 Explaining Uncertainty (±)

When you see a value like 16.5 ± 0.3 °C , the ± 0.3 is the uncertainty. It tells us the range of the results.

✅ 02.5 Answer

It is the uncertainty because 0.3°C is the range about the mean value.

Note: You can also show this by showing that 16.8 (max) and 16.2 (min) are both 0.3 away from the mean 16.5.

2 Marks

✅ 02.6 Answer

Random error

1 Mark

❌ Error Types Explained

  • Random Error: Results vary in an unpredictable way. This is why we take repeats and calculate a mean. (Correct for Table 3).
  • Systematic Error: Results are consistently off by the same amount every time (e.g., a balance that isn't zeroed).
  • Zero Error: A type of systematic error where the equipment gives a reading when it should be zero.

Summary Checklist for RPA4

  • ✅ Use a polystyrene cup and a lid to provide insulation and reduce heat loss to the surroundings.
  • ✅ Always record the initial and final (or lowest/highest) temperature.
  • ✅ Independent variable is usually the mass of reactant or volume of solution.
  • ✅ Endothermic = Temp Down | Exothermic = Temp Up.

Topics

Chemistry · Required Practicals · Required Practicals · C5: Energy Changes

Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Higher), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.