AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2024: Question 2

10 marks · Low Demand difficulty · Short Answer

Identify apparatus and indicators for a neutralisation titration, read a burette, select concordant titration results to calculate a mean, and determine the formula of barium chloride.

Practise this question

Question

Question 2 illustrates a titration practical. Figure 4 shows Step 1 (alkali measured into a conical flask using a volumetric pipette) and Step 2 (acid delivered into the conical flask from a burette). Sub-questions ask to name apparatus A, B, and C, name an indicator, give the observation for neutralisation, and give two ways to ensure accurate volume measurement. Figure 5 shows a zoomed-in section of a burette between 16 and 18 cm³ showing the meniscus resting at 16.6 cm³. Table 1 lists titration results of 25.3, 23.7, and 23.6 cm³, asking which two results should be used for the mean. The final part asks for the chemical formula of barium chloride given barium 2-plus and chloride 1-minus ions.
Question text

02 A titration measures the volumes of an acid and an alkali that neutralise each other.

Figure 4 shows the apparatus used.

Figure 4

02.1 Name the pieces of equipment labelled A, B and C in Figure 4.

Choose answers from the box.

[3 marks]

beaker burette conical flask

measuring cylinder pipette test tube

A

B

C

In Step 2 in Figure 4 the acid is added to the alkali until the solution is neutralised.

The volume of acid added is then read from equipment C.

02.2 Name a suitable indicator for use in Step 2 of the titration.

[1 mark]

02.3 Give one observation that shows the alkali is neutralised.

[1 mark]

02.4 Give two ways to make sure that the volume of acid added is accurate.

[2 marks]

02.5 Figure 5 shows the reading on equipment C at the end of Step 2.

Figure 5

What is the reading on equipment C in Figure 5?

[1 mark]

Tick ( ) one box.

16.4 cm3

16.6 cm3

17.4 cm3

17.6 cm3

02.6 A student did a different titration.

Table 1 shows the results.

Table 1

Trial 1 Trial 2 Trial 3

Volume of acid added in cm3 25.3 23.7 23.6

Which two results should be used to calculate the mean volume of acid added?

[1 mark]

Tick ( ) one box.

Trial 1 and Trial 2

Trial 1 and Trial 3

Trial 2 and Trial 3

02.7 A salt is produced when an acid neutralises an alkali.

Barium chloride is a salt containing the ions Ba2+ and Cl¯

What is the formula of barium chloride?

[1 mark]

Tick ( ) one box.

BaCl BaCl2 Ba2Cl Ba2Cl2

Mark scheme

Show the mark scheme Mark scheme for Question 2 with total 10 marks: 02.1 requires (A) pipette, (B) conical flask, (C) burette (3 marks); 02.2 accepts methyl orange or phenolphthalein, allows litmus, rejects universal indicator (1 mark); 02.3 accepts colour change (1 mark); 02.4 awards 2 marks for any two from: swirl, add acid drop by drop, read burette at eye level/bottom of meniscus, ensure no bubbles in burette, use a white tile, repeat and take a mean; 02.5 gives 1 mark for 16.6 cm³; 02.6 gives 1 mark for Trial 2 and Trial 3; 02.7 gives 1 mark for BaCl₂.

Question 2

AO /

Question Answers Extra information Mark

Spec. Ref.

02.1 (A) pipette 1 AO1

4.4.2.5

(B) conical flask 1 RPA2

(C) burette 1

AO /

Spec. Ref.

02.2 methyl orange (solution) allow litmus (solution) 1 AO1

or 4.4.2.5

phenolphthalein (solution) RPA2

do not accept universal

indicator

AO /

Spec. Ref.

02.3 colour change ignore clear 1 AO1

4.4.2.5

RPA2

AO /

Spec. Ref.

02.4 any two from: 2 AO1

• swirl 4.4.2.5

• add the acid drop by drop RPA2

• read (burette) at eye level allow read (burette) at the

bottom of the meniscus

• ensure no bubbles in burette

• use a white tile

• repeat and take a mean

AO /

Spec. Ref.

3 AO2

16.6 cm 1

02.5 – – – 4.4.2.5

RPA2

10 AO /

Spec. Ref.

02.6 trial 2 and trial 3 1 AO3

4.4.2.5

RPA2

AO /

Spec. Ref.

02.7 BaCl2 1 AO2

4.1.1.1

4.4.2.2

Total Question 2 10

How to answer it

Required Practical 2: Neutralisation & Titration Method

📋 What this question tests

This question assesses core practical skills and foundational chemical knowledge from Topic 4 (Chemical Changes) and Topic 1 (Atomic Structure and the Periodic Table):

  • Identifying standard titration glassware (pipette, conical flask, burette).
  • Selecting suitable single-change indicators vs wide-range indicators.
  • Practical steps taken to maximise accuracy and precision during a titration.
  • Reading inverted burette scales correctly to 0.1 cm³.
  • Selecting concordant results to calculate an accurate mean titre.
  • Deducing the formula of an ionic compound by balancing ionic charges.

Part 02.1: Identifying Titration Apparatus

Apparatus Identification • 3 Marks

✅ Correct Labels

  • A: pipette [1 mark]
  • B: conical flask [1 mark]
  • C: burette [1 mark]

💡 Equipment Functions

  • Volumetric Pipette: Accurately measures one fixed volume (usually 25.0 cm³) of alkali into the flask.
  • Conical Flask: Sloped sides allow safe swirling without spilling.
  • Burette: Adds variable, measured volumes of acid drop by drop.
Examiner Insight: Spelling counts for precision, but phonetic spellings of "pipette" and "burette" are usually credited. Do not confuse a measuring cylinder with a pipette or burette; cylinders are not precise enough for titrations.

Parts 02.2 & 02.3: Titration Indicators & End-Point

Indicator Choice & Observation • 2 Marks

✅ Correct Answers

02.2 Suitable Indicator:

  • Phenolphthalein (solution) OR
  • Methyl orange (solution) OR
  • Litmus (solution) [1 mark]

02.3 Observation at Neutralisation:

  • Colour change [1 mark]

❌ Common Errors

  • Universal Indicator: Strictly NOT accepted. Universal indicator changes colour gradually over a wide pH range, making it impossible to see a sharp, distinct end-point.
  • Stating "it goes clear": Saying "colourless" is acceptable for phenolphthalein, but never write "clear" — "clear" means transparent, not colourless! Writing simply colour change guarantees the mark.

🧠 Exam Technique: Remember the Colours

  • Phenolphthalein: Pink in alkali → Colourless in acid.
  • Methyl orange: Yellow in alkali → Red in acid (orange at the exact end-point).

Part 02.4: Improving Accuracy in Titration

Practical Procedures • 2 Marks

✅ Correct Answers (Choose Any Two)

  • Swirl the conical flask during addition.
  • Add the acid drop by drop (slowly near the end-point).
  • Read the burette at eye level (to avoid parallax error).
  • Read from the bottom of the meniscus.
  • Place a white tile under the flask (to see colour change clearly).
  • Ensure there are no air bubbles in the burette tip.
  • Repeat the titration and calculate a mean of concordant results.

🧠 Exam Technique: Action & Reason

Questions asking how to make a practical "more accurate" always test procedural details:

  • Swirling ensures the acid and alkali mix thoroughly.
  • Adding dropwise prevents adding excess acid past the true neutralisation point.
  • "Repeat" alone is not always enough; standard best practice is to write "repeat and calculate a mean".

Part 02.5: Reading a Burette Scale

Scale Reading • 1 Mark

✅ Correct Answer

Selected option: 16.6 cm³ [1 mark]

❌ Common Error: Reading Upwards

Students frequently answer 17.4 cm³ because they read from the bottom upwards (like a measuring cylinder).

  • A burette measures delivered volume, so zero is at the top.
  • Numbers increase downwards: 16 is above 17.
  • Counting down from 16.0: six small marks down gives 16.6 cm³.

Part 02.6: Selecting Results for a Mean

Data Handling: Concordance • 1 Mark

✅ Correct Selection

Selected option: Trial 2 and Trial 3 [1 mark]

📐 Identifying Concordant Titres

Trial 1 Trial 2 Trial 3
25.3 cm³ (Rough) 23.7 cm³ 23.6 cm³
  • Concordant results are titres within 0.10 cm³ of each other.
  • |23.7 − 23.6| = 0.10 cm³ (Concordant).
  • Trial 1 (25.3 cm³) is an anomalous/rough titration and must be discarded.

Part 02.7: Deducing the Formula of Barium Chloride

Ionic Formulae • 1 Mark

✅ Correct Answer

Selected option: BaCl₂ [1 mark]

📐 Balancing Ionic Charges Step-by-Step

  1. Identify ion charges: Barium = Ba²⁺, Chloride = Cl⁻.
  2. Compounds must have an overall charge of 0 (neutral).
  3. Each Ba²⁺ gives a charge of +2.
  4. To balance +2, you need two Cl⁻ ions: 2 × (−1) = −2.
  5. Ratio: 1 Ba²⁺ to 2 Cl⁻ → Formula is BaCl₂.

Topics

Chemistry · Required Practicals · C4: Chemical Changes · C2: Bonding, Structure and the Properties of Matter · Required Practicals

Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Foundation), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.