AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2025: Question 4

10 marks · Low Demand difficulty · Short Answer

Identify the experimental apparatus and method for a titration, calculate the mean titre excluding anomalous results to three significant figures, and identify the ions present in acids and alkalis.

Practise this question

Question

Question 4 describes a neutralisation experiment where 25.0 cm³ of alkali is titrated with acid using indicator substance X and a conical flask on a white tile. Sub-questions include: 04.1 ticking the experiment name from four options; 04.2 naming substance X; 04.3 choosing the equipment used to add acid (Beaker, Burette, Test tube); 04.4 suggesting an improvement to step 4; 04.5 calculating the mean volume from Table 3 (Trial 1 = 8.95, Trial 2 = 9.00, Trial 3 = 8.85, Trial 4 = 8.45 cm³) to 3 significant figures excluding the anomaly; and 04.6 drawing lines matching 'Acid' and 'Alkali' to their respective characteristic aqueous ions (Cl⁻, H⁺, Na⁺, OH⁻).
Question text

04 A student did an experiment to find the volume of an acid that neutralised

25.0 cm3 of an alkali.

This is the method used.

1. Measure 25.0 cm3 of the alkali into a conical flask.

2. Add a few drops of substance X to the alkali.

3. Place the conical flask on a white tile.

4. Add the acid to the alkali until a colour change is seen.

5. Measure the volume of acid added.

6. Repeat steps 1 to 5 three more times.

04.1 What is the name of this experiment?

[1 mark]

Tick ( ) one box.

Crystallisation

Distillation

Electrolysis

Titration

04.2 Substance X is used in step 2 of the method.

What type of substance is X?

[1 mark]

04.3 Which piece of equipment is used to add the acid to the alkali in step 4?

[1 mark]

Tick ( ) one box.

Beaker

Burette

Test tube

04.4 Suggest one improvement to step 4 of the method.

[1 mark]

04.5 Table 3 shows the results.

Table 3

Trial 1 Trial 2 Trial 3 Trial 4

Volume of acid in cm3 8.95 9.00 8.85 8.45

Calculate the mean volume of the acid needed to neutralise 25.0 cm3 of the alkali.

Give your answer to 3 significant figures.

Do not include the anomalous result.

[4 marks]

Mean volume (3 significant figures) =17 cm3

04 *.156Aqueous solutions of acids and alkalis contain ions.*

Draw one line from each type of aqueous solution to the ion that is always in the

aqueous solution.

[2 marks]

Type of aqueous solution Ion

Cl–

Acid H+

Na+

Alkali

*16* –

OH

Mark scheme

Show the mark scheme Mark scheme for Question 4: 04.1 awards 1 mark for 'titration'. 04.2 awards 1 mark for 'indicator'. 04.3 awards 1 mark for 'burette'. 04.4 awards 1 mark for 'add the acid dropwise (near the end point)' or 'swirl the flask'. 04.5 awards 4 marks for identifying and using only trials 1, 2, and 3 (8.95, 9.00, 8.85), calculating the mean (26.80 / 3 = 8.933333 cm³), and rounding correctly to 8.93 cm³. 04.6 awards 2 marks for drawing lines connecting Acid to H⁺ and Alkali to OH⁻.

Question 4

AO /

Question Answers Extra information Mark

Spec. Ref.

04.1 titration 1 AO1

4.4.2.5

RPA 2

AO /

Spec. Ref.

04.2 indicator allow any named indicator 1 AO1

4.4.2.5

RPA 2

AO /

Spec. Ref.

04.3 burette 1 AO1

4.4.2.5

RPA 2

AO /

Spec. Ref.

04.4 add the acid dropwise (near the 1 AO3

end point) 4.4.2.5

or RPA 2

swirl the flask

AO /

Spec. Ref.

04.5 use of 8.95, 9.00 and 8.85 only 1 AO3

(mean volume = ) allow (mean volume = )

8.95 + 9.00 + 8.85 26.80 1 AO2

allow correct use of incorrect

values of volume

= 8.933333 (cm3) 1 AO2

12 3

= 8.93 (cm ) allow an answer correctly 1 AO2

rounded to 3 significant figures

from an incorrect calculation

which uses the values 4.4.2.5

in the question RPA 2

AO /

Question Answers Mark

Spec. Ref.

04.6

1 AO1

4.4.2.4

do not accept more than one line from a box on the left

Total Question 4 10

How to answer it

Acid-Base Titration & Neutralisation Ions

What This Question Tests

This question assesses practical understanding from AQA Required Practical 2 (Neutralisation / Titration) and the core theory of aqueous acids and alkalis:

  • Naming the experimental technique and standard titration apparatus ( burette ).
  • Understanding the function of an indicator to determine the end-point.
  • Suggesting procedural refinements to improve precision and accuracy.
  • Calculating a concordant mean volume, spotting an anomalous titre, and rounding to 3 significant figures .
  • Identifying the characteristic ions present in aqueous solutions of acids ( H⁺ ) and alkalis ( OH⁻ ).

Part 04.1 — Identifying the Practical Method

1 Mark • AO1 • Specification 4.4.2.5 (RPA 2)

✅ Correct Answer

Titration [1 mark]

💡 Key Knowledge

A titration is an accurate quantitative experimental method used to determine the exact volume of an acid needed to neutralise a known volume of an alkali (or vice versa).

Examiner Insight: Distillation separates liquids by boiling point, crystallisation produces solid crystals from solutions, and electrolysis uses electricity to decompose ionic compounds. None of these involve finding neutralisation volumes.

Part 04.2 — Role of Substance X

1 Mark • AO1 • Specification 4.4.2.5 (RPA 2)

✅ Correct Answer

Indicator [1 mark]

(Also allowed: any named indicator such as phenolphthalein, methyl orange, or litmus.)

🧠 Exam Technique

The question asks "what type of substance is X?". Giving the generic category indicator is the safest and clearest way to secure the mark.

❌ Common Errors

  • Naming "Universal Indicator" — while it is an indicator, universal indicator is unsuitable for accurate titrations because it has a gradual colour change rather than a sharp end-point.
  • Confusing an indicator with a catalyst.

Part 04.3 — Apparatus for Variable Addition

1 Mark • AO1 • Specification 4.4.2.5 (RPA 2)

✅ Correct Answer

Burette [1 mark]

💡 Equipment Roles

  • Volumetric Pipette: Measures one single, fixed volume accurately (e.g. 25.0 cm³ alkali in Step 1).
  • Burette: Adds variable volumes accurately drop-by-drop and measures the total volume delivered (Step 4).

Part 04.4 — Improving the Experimental Procedure

1 Mark • AO3 • Specification 4.4.2.5 (RPA 2)

✅ Correct Answer (Any one of the following)

  • Add the acid dropwise (near the end point) [1 mark]
  • Swirl the flask (continually during addition) [1 mark]

🧠 Why These Improvements Matter

  • Adding dropwise: Prevents adding excess acid past the exact point of neutralisation (the end-point).
  • Swirling: Ensures complete mixing of acid and alkali so that the colour change represents the whole solution.

❌ What Examiners Reject

Vague statements such as "do it more carefully", "add it slower" (without specifying drops), or suggestions already completed in the method (e.g. "use a white tile" or "repeat it").

Part 04.5 — Calculating Mean Volume

4 Marks • AO2 / AO3 • Specification 4.4.2.5

📐 Step-by-Step Calculation

  1. Identify and exclude the anomaly:
    Looking at the titres: Trial 1 = 8.95, Trial 2 = 9.00, Trial 3 = 8.85, Trial 4 = 8.45 cm³.
    Trial 4 (8.45 cm³) is far lower than the others and must be discarded.
    Use 8.95, 9.00, and 8.85 only. [Mark 1]
  2. Set up the mean calculation:
    Mean = (8.95 + 9.00 + 8.85) / 3 = 26.80 / 3 [Mark 2]
  3. Calculate the unrounded value:
    Mean = 8.933333... cm³ [Mark 3]
  4. Round to 3 significant figures (as instructed):
    First 3 non-zero digits are 8, 9, 3. The next digit is 3 (rounds down).
    Final answer = 8.93 cm³ [Mark 4]

❌ Common Traps

  • Including all four values: (8.95 + 9.00 + 8.85 + 8.45) / 4 = 8.8125 cm³. This loses Mark 1.
  • Incorrect rounding: Leaving the answer as 8.9 (2 s.f.) or 8.933 (4 s.f.) loses the final mark.
  • Dividing by 4: Even if only three numbers are added, dividing by 4 instead of 3 is a common error.

🧠 Exam Tip

Even if you make a simple addition error, write down your full working! Marks in multi-step calculations are awarded for working, and an "error carried forward" rule applies to the rounding mark if you correctly round your own value to 3 s.f.

Part 04.6 — Characteristic Ions in Solution

2 Marks • AO1 • Specification 4.4.2.4

✅ Correct Matching

Type of Aqueous Solution Ion Always Present
Acid ➔ H⁺ [1 mark]
Alkali ➔ OH⁻ [1 mark]

💡 Key Knowledge

  • Acids: Form hydrogen ions (H⁺) when dissolved in water.
  • Alkalis: Form hydroxide ions (OH⁻) when dissolved in water.
  • Neutralisation ionic equation:
    H⁺(aq) + OH⁻(aq) ➔ H₂O(l)

❌ Trap to Avoid

Cl⁻ and Na⁺ are only present if you specifically use hydrochloric acid and sodium hydroxide. They are not present in all acids or all alkalis! Also, note the rubric: "do not accept more than one line from a box on the left".

Topics

Chemistry · Required Practicals · C4: Chemical Changes · Required Practicals

Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Foundation), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.