AQA GCSE Chemistry Chemistry Paper 1 (Foundation), November 2020: Question 7
11 marks · Standard Demand difficulty · Short Answer
Answer questions on acids, bases, naming salts, interpreting a titration pH curve, calculating percentage uncertainty, and apparatus precision.
Practise this questionQuestion
Question text
07 This question is about acids, bases and salts.
Zinc nitrate is a salt.
A student produces zinc nitrate using an acid and a base.
07.1 Which acid should the student use to produce zinc nitrate?
[1 mark]
Tick ( ) one box.
Hydrochloric acid
Nitric acid
Sulfuric acid
07.2 Which is a base the student could use to produce zinc nitrate?
[1 mark]
Tick ( ) one box.
Zinc chloride
Zinc oxide
Zinc sulfate
07.3 Name the salt with the formula MgBr2
[1 mark]
A student investigated how pH changes during a titration.
This is the method used.
1. Pour 25.0 cm3 of hydrochloric acid into a beaker.
2. Measure the pH of the hydrochloric acid with a pH probe.
*25* 3. Add 1.0 cm3 of sodium hydroxide solution from a burette.
4. Swirl the mixture.
5. Measure the pH of the mixture.
6. Repeat steps 3 to 5 until a total of 30.0 cm3 of sodium hydroxide solution has been
added.
Figure 10 shows the student’s results.
Figure 10
07.4 Describe how the pH of the mixture changes as sodium hydroxide solution is added to
hydrochloric acid.
Use data from Figure 10 in your answer.
[3 marks]
07.5 What volume of sodium hydroxide solution is needed to neutralise 25.0 cm3 of
hydrochloric acid?
Use Figure 10.
[1 mark]
Volume = cm3
07.6 Figure 11 shows the colour of universal indicator at different pH values.
Figure 11
The student could have used universal indicator instead of a pH probe.
Determine the colour of universal indicator when 10.0 cm3 of
sodium hydroxide solution has been added to 25.0 cm3 of hydrochloric acid.
Use Figure 10 and Figure 11.
[1 mark]
Colour = 28
07.7 The student used a pipette to measure 25.0 cm3 of hydrochloric acid.
Figure 12 shows a pipette.
*27* Figure 12
The pipette is labelled 25.0 ± 0.06 cm3
Calculate the percentage uncertainty in the volume measured using this pipette.
Use the equation:
uncertainty
percentage uncertainty = × 100
volume measured
[2 marks]
Percentage uncertainty = %
07.8 Give one advantage of using a pipette rather than using a measuring cylinder to
measure the volume of hydrochloric acid.
[1 mark]
Mark scheme
Show the mark scheme
Question 7
AO /
Question Answers Extra information Mark
Spec. Ref.
07.1 nitric acid 1 AO2
4.4.2.2
RPA 1
07.2 zinc oxide 1 AO2
4.4.2.2
RPA 1
07.3 magnesium bromide 1 AO2
4.1.1.1
07.4 allow a tolerance of 1 cm3 on AO2
volumes 4.4.2.4
allow a tolerance of 0.2 on pH
values
(from 0) to 20 cm3 the pH allow increase from pH 1 to 1
increases (gradually) pH 3
at 20 cm3 the pH changes from allow sudden / steep increase at 1
pH 3 to pH 11 20 cm3
allow sudden / steep increase
from pH 3 to pH 11
from 20 cm3 the pH increases allow (gradual) increase from pH 1
(gradually) 11
if no other marks awarded allow
1 mark for a description of the
three stages with no values
used.
Question 7 continued
AO /
Spec. Ref.
07.5 20 (cm3) allow 20.0 (cm3) 1 AO3
17 4.4.2.4
07.6 red 1 AO3
4.4.2.4
07.7 AO2
0.06 1 4.4.2.5
× 100
25(.0)
= 0.24 (%) 1
07.8 (pipette) measures volume more allow (pipette is) more accurate 1 AO3
accurately 4.4.2.5
or RPA 2
(pipette has a) smaller
(percentage) uncertainty
Total 11
How to answer it
Acids, Bases, Titration Curves & Apparatus Uncertainty
What this question tests
This question assesses core skills across chemical naming, acid-base neutralisation, practical data interpretation, and quantitative experimental accuracy:
- Identifying which specific acids and bases react to form named salts.
- Naming binary ionic salts correctly from chemical formulae.
- Describing three distinct regions of a pH titration curve using accurate coordinates and data.
- Identifying the equivalence (neutralisation) volume on a pH curve.
- Reading indicator colour scales against graphical pH values.
- Calculating percentage uncertainty for volumetric glassware and evaluating equipment precision.
Choosing the Acid to Make Zinc Nitrate
Identify the correct acid required to produce zinc nitrate
✅ Correct Answer
Nitric acid (Tick box 2)
💡 Key Knowledge
- Hydrochloric acid forms chlorides.
- Nitric acid forms nitrates.
- Sulfuric acid forms sulfates.
Choosing the Base to Make Zinc Nitrate
Identify an insoluble base containing zinc
✅ Correct Answer
Zinc oxide (Tick box 2)
❌ Common Errors
Zinc chloride and zinc sulfate are already salts, not bases. Bases are typically metal oxides, metal hydroxides, or metal carbonates.
Naming the Salt from its Formula
State the chemical name for MgBr₂
✅ Correct Answer
Magnesium bromide
🧠 Exam Technique
- The metal name comes first and stays unchanged: Mg = magnesium.
- A non-metal in a simple binary salt changes its ending to -ide: bromine becomes bromide.
- Do not include numbers like "di-" (e.g. magnesium dibromide is incorrect for ionic compounds).
Describing the pH Titration Curve
Describe how the pH changes as NaOH is added, using data from Figure 10
✅ Model Answer (3 Distinct Stages)
- Stage 1 (Initial gradual rise): From 0 to 20 cm³ of NaOH added, the pH increases slowly/gradually (from pH 1 to pH 3).
- Stage 2 (Vertical neutralisation inflection): At 20 cm³, there is a sudden, steep increase in pH from pH 3 to pH 11.
- Stage 3 (Final plateau): From 20 cm³ onwards (up to 30 cm³), the pH increases gradually / levels off (around pH 11 to 13).
Tolerances allowed: ±1 cm³ on volumes, ±0.2 on pH values.
Partial credit: If no numbers are quoted, a maximum of 1 mark is awarded for describing all three stages qualitatively.
🧠 Top-Level Exam Strategy
Whenever asked to describe a graph that has inflection points:
- Break the curve into three parts: before the steep section, during the steep jump, and after the jump.
- Quote both the volume (x-axis) and pH (y-axis) ranges for each part.
- Words like "sudden", "steep", or "vertical jump" are essential for describing what happens at exactly 20 cm³.
Finding the Neutralisation Volume
Determine the volume of NaOH needed to neutralise 25.0 cm³ of HCl
✅ Correct Answer
20 cm³ (or 20.0 cm³)
💡 How to Read the Curve
Neutralisation means reaching pH 7. Trace horizontally across from pH 7 on the y-axis to the curve: it intersects the vertical line precisely at 20 cm³.
Determining Indicator Colour
Find the colour of universal indicator after 10.0 cm³ of NaOH is added
✅ Correct Answer
Red
🧠 Two-Step Chart Reading
- Find 10.0 cm³ on the x-axis of Figure 10 and read up to the line: the pH is approximately 1.5.
- Look at Figure 11: pH values 0, 1, and 2 are labelled Red.
Calculating Percentage Uncertainty
Calculate the percentage uncertainty for a pipette labelled 25.0 ± 0.06 cm³
📐 Step-by-Step Calculation
Formula given:
- Substitute values:
Uncertainty = 0.06 cm³
Volume measured = 25.0 cm³
(0.06 / 25.0) × 100 [1 mark] - Calculate final value:
0.0024 × 100 = 0.24% [1 mark]
❌ Common Calculation Traps
- Forgetting to multiply by 100: Writing 0.0024 instead of 0.24%.
- Inverting the fraction: Dividing 25 by 0.06 gives 416.7%, which is an impossible uncertainty for standard lab glassware!
Evaluating Practical Equipment
Give one advantage of using a volumetric pipette rather than a measuring cylinder
✅ Accepted Answers (Either of the following)
- A pipette measures volume more accurately (or is more precise).
- A pipette has a smaller percentage uncertainty (or smaller uncertainty).
❌ Vague Statements to Avoid
- "It is easier to use" / "It is quicker" → 0 marks.
- "It prevents human error" → 0 marks (you can still misread a meniscus on a pipette).
- Always focus on accuracy, resolution, or lower uncertainty when comparing volumetric glassware to cylinders.
Topics
Chemistry · Required Practicals · C1: Atomic Structure and the Periodic Table · C3: Quantitative Chemistry · C4: Chemical Changes · Required Practicals
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Foundation), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.