AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2023: Question 2
10 marks · Low Demand difficulty · Short Answer
Identify the ions produced by acids and alkalis, answer questions on a titration experiment to find reacting volumes, and calculate the mass of solute in a given volume.
Practise this questionQuestion
Question text
02 This question is about acids and alkalis.
02.1 Acids and alkalis are substances that produce ions in aqueous solution.
Draw one line from each substance to the ion always produced by that substance in
aqueous solution.
[2 marks]
Ion always produced in
Substance
aqueous solution
Cl−
H+
Acid
Na+
Alkali
OH−
SO 2−
02.2 What type of aqueous solution has a pH of 11?
[1 mark]
Tick ( ) one box.
Acidic
Alkaline
Neutral 6
A student determined the reacting volumes of hydrochloric acid and
sodium hydroxide solution by titration.
This is the method used.
1. Measure 25.0 cm3 of the sodium hydroxide solution.
2. Add the sodium hydroxide solution to a conical flask.
3. Add 3 drops of indicator to the sodium hydroxide solution.
4. Add the hydrochloric acid drop by drop until the indicator changes colour.
5. Record the volume of the hydrochloric acid added.
6. Repeat steps 1 to 5 three more times.
02.3 Which piece of equipment should be used to measure 25.0 cm3 of
the sodium hydroxide solution in step 1?
[1 mark]
Tick ( ) one box.
Beaker
Pipette
Ruler
02.4 Which piece of equipment should be used to add the hydrochloric acid drop by drop in
step 4?
[1 mark]
Tick ( ) one box.
Balance
Burette
Measuring cylinder 7
Table 1 shows the results.
Table 1
Trial 1 2 3 4
Volume of hydrochloric acid
3 24.3 24.5 28.1 24.4
added in cm
02.5 Which is the anomalous result in Table 1?
[1 mark]
Trial 1 Trial 2 Trial 3 Trial 4
02.6 Suggest one reason for the anomalous result in Table 1.
[1 mark]
02.7 The student used a solution of sodium hydroxide of concentration 4.00 g/dm3.
Calculate the mass of sodium hydroxide in 25.0 cm3 of this solution.
1 dm3 = 1000 cm3
[3 marks]
Mass = g
Mark scheme
Show the mark scheme
AO /
Question Answers Mark
Spec. Ref.
02.1 AO1
4.4.2.4
do not accept more than one line from a box on the left
AO /
Question Answers Extra information Mark
Spec. Ref.
02.2 alkaline 1 AO1
4.4.2.4
AO /
Spec. Ref.
02.3 pipette 1 AO1
4.4.2.5
RPA2
AO /
Spec. Ref.
02.4 burette 1 AO1
4.4.2.5
– HEMISTRY – – RPA2
AO /
Spec. Ref.
02.5 trial 3 1 AO3
4.4.2.5
RPA2
AO /
Spec. Ref.
02.6 any one from: 1 AO3
• (hydrochloric acid) not added 4.4.2.5
drop by drop
• did not swirl
• did not rinse apparatus (after
previous trial)
• did not use a white tile
• misread pipette / burette
allow measured out too much
alkali
AO /
Spec. Ref.
02.7 3 25.0 3 1 AO2
(25.0 cm = =) 0.025 (dm ) 4.3.2.5
1000
(mass =) 0.025 × 4.00 allow correct use of incorrect / 1
no conversion of volume
= 0.1 (g) 1
alternative approach:
4.00
(concentration = = )
1000
0.004 (g/cm3) (1)
(mass =) 0.004 × 25.0 (1) allow correct use of incorrectly
determined concentration in
g/cm3
= 0.1 (g) (1)
– HEMISTRY – –
Total Question 2 10
Question 3
How to answer it
Acids, Alkalis & Titration Calculations
AQA GCSE Chemistry: Required Practical 2 & Chemical Changes
- Recall of fundamental ions that define acids (H⁺) and alkalis (OH⁻) in aqueous solutions.
- Interpreting the pH scale to classify acidic, neutral, and alkaline solutions.
- Selection of correct laboratory apparatus (pipette vs burette) for precise volumetric analysis.
- Identifying anomalous data points in repeating titration trials and identifying sources of experimental error.
- Calculating the mass of solute using concentration in g/dm³ and converting volume units (cm³ to dm³).
Characteristic Ions of Acids and Alkalis
Draw one line from each substance to the ion always produced in aqueous solution
✅ Correct Answer
- Acid ➔ connects to H⁺ [1 mark]
- Alkali ➔ connects to OH⁻ [1 mark]
💡 Key Knowledge
By definition in water:
- Acids produce hydrogen ions ( H⁺ ).
- Alkalis are soluble bases that produce hydroxide ions ( OH⁻ ).
- Neutralisation reaction: H⁺ + OH⁻ ➔ H₂O .
❌ Common Errors
- Drawing multiple lines from one box: The mark scheme specifies "do not accept more than one line from a box on the left". If you draw two lines from "Acid", you lose the mark for that substance.
- Selecting specific salt ions like Cl⁻ or Na⁺ , which are only present in specific substances (e.g. HCl or NaOH), not all acids/alkalis.
pH Scale Interpretation
What type of aqueous solution has a pH of 11?
✅ Correct Answer
Tick (✔) the box next to: Alkaline [1 mark]
💡 Key Knowledge
- pH 0 – 6: Acidic (pH 1–2 is strongly acidic; pH 5–6 is weakly acidic)
- pH 7: Neutral (pure water at 25 °C)
- pH 8 – 14: Alkaline (pH 11–14 is strongly alkaline)
🧠 Exam Technique
Ensure you tick only one box. If you accidentally mark two, cross out the incorrect one clearly and initial it.
Titration Apparatus Selection
Choosing the correct volumetric equipment for accurate measurements
✅ Correct Answers
02.3: Measure 25.0 cm³ sodium hydroxide ➔ Pipette [1 mark]
02.4: Add hydrochloric acid drop by drop ➔ Burette [1 mark]
💡 Equipment Functions
- Volumetric Pipette: Measures one single, exact fixed volume (typically 25.0 cm³) with extremely high accuracy.
- Burette: Has a graduated scale and a tap, allowing precise, variable volumes to be added drop by drop until an endpoint is reached.
- Beaker / Measuring Cylinder: Too crude and inaccurate for titration standards.
❌ Common Errors
- Confusing the two names: writing that acid is added from a pipette and alkali measured with a burette.
- Choosing "measuring cylinder" for step 4: a measuring cylinder has no tap, making dropwise control impossible.
Analysing Titration Results & Sources of Error
Identifying an anomaly in Table 1 and suggesting a valid laboratory cause
✅ Correct Answers
02.5: Anomalous result: Trial 3 [1 mark]
02.6: Suggest one reason for this anomaly: [1 mark]
Any one from:
- Acid was not added drop by drop (overshot the endpoint).
- Did not swirl the flask while adding acid.
- Did not rinse apparatus after the previous trial.
- Did not use a white tile (harder to see colour change promptly).
- Misread the pipette or burette scale.
- Measured out too much alkali (NaOH) into the flask.
🧠 Identifying Anomalies
Look at the volumes added:
- Trial 1 = 24.3 cm³
- Trial 2 = 24.5 cm³
- Trial 3 = 28.1 cm³ ➔ Anomalous! (Over 3.5 cm³ higher)
- Trial 4 = 24.4 cm³
Trials 1, 2, and 4 are concordant (within 0.20 cm³ of each other).
❌ Common Errors
- Vague answers like "human error" or "student did it wrong" get 0 marks. You must state a specific practical mistake.
- Suggesting reasons that would result in a lower volume (e.g. "not enough alkali was added") when Trial 3 required significantly more acid.
Mass Concentration Calculation
Calculate the mass of sodium hydroxide in 25.0 cm³ of a 4.00 g/dm³ solution
📐 Step-by-Step Calculation
Divide by 1000:
Volume = 25.0 / 1000 = 0.025 dm³
Mass (g) = Concentration (g/dm³) × Volume (dm³)
Mass = 4.00 × 0.025
Mass = 0.1 g (or 0.10 g)
💡 Alternative Valid Method
Convert concentration to g/cm³ first:
- Concentration = 4.00 / 1000 = 0.004 g/cm³ [1 mark]
- Mass = 0.004 × 25.0 [1 mark]
- Answer = 0.1 g [1 mark]
❌ Common Errors & Pitfalls
- Forgetting to convert units: Calculating 4.00 × 25.0 = 100 g . 25 cm³ is a tiny volume (approx. two tablespoons)—it cannot contain 100 grams of solute!
- Multiplying by 1000 instead of dividing: Calculating 25.0 × 1000 = 25 000 . Remember that 1 dm³ = 1000 cm³, so cm³ must always be divided by 1000 to get dm³.
- Error-Carried-Forward (ECF): If you do the conversion incorrectly, you can still gain marks for correctly multiplying your incorrect volume by 4.00.
Topics
Chemistry · Required Practicals · C4: Chemical Changes · C3: Quantitative Chemistry · Required Practicals
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Foundation), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.