AQA GCSE Chemistry Chemistry Paper 1 (Foundation), November 2020: Question 9
11 marks · Standard Demand difficulty · Extended Answer
Identify properties of transition metals, explain displacement of silver by copper, plan an investigation to identify unknown metals using dilute acid, and calculate the relative atomic mass of an element from isotopic abundance.
Practise this questionQuestion
Question text
09 This question is about metals and the reactivity series.
09.1 Which two statements are properties of most transition metals?
[2 marks]
Tick ( ) two boxes.
They are soft metals.
They form colourless compounds.
They form ions with different charges.
They have high melting points.
They have low densities.
09.2 A student added copper metal to colourless silver nitrate solution.
The student observed:
• pale grey crystals forming
• the solution turning blue.
Explain how these observations show that silver is less reactive than copper.
[3 marks]
09.3 A student is given three metals, X, Y and Z to identify.
The metals are magnesium, iron and copper.
Plan an investigation to identify the three metals by comparing their reactions with
dilute hydrochloric acid.
*32* Your plan should give valid results.
[4 marks]
09.4 Metal M has two isotopes.
Table 6 shows the mass numbers and percentage abundances of the isotopes.
Table 6
Mass number Percentage abundance (%)
203 30
205 70
Calculate the relative atomic mass (Ar) of metal M.
Give your answer to 1 decimal place.
[2 marks]
Relative atomic mass (1 decimal place) =
Mark scheme
Show the mark scheme
Question 9
AO /
Question Answers Extra information Mark
Spec. Ref.
09.1 they form ions with different 1 AO1
charges 4.1.3.1
4.1.3.2
they have high melting points 1
09.2 the (grey) crystals are silver 1 AO3
4.4.1.2
the copper ions (produced) are allow the copper nitrate / 1
blue compound (produced) is blue
(because) copper displaces 1
silver
Question 9 continued
AO/
Question Answers Mark
Spec. Ref
Level 2: The method would lead to the production of a valid AO1
09.3 3–4
outcome. The key steps are identified and logically sequenced. AO3
4.4.1.2
Level 1: The method would not lead to a valid outcome. Some 4.5.1.1
1–2
relevant steps are identified, but links are not made clear. RPA 4
No relevant content 0
Indicative content
Key steps
• add the metals to (dilute) hydrochloric acid
• measure temperature change
or
compare rate of bubbling
or
compare colour of resulting solution
for copper:
• no reaction
• shown by no temperature change
or
shown by no bubbles
for magnesium and iron:
• magnesium increases in temperature more than iron
or
magnesium bubbles faster than iron
or
magnesium forms a colourless solution and iron forms a coloured
solution
Control variables
• same concentration / volume of hydrochloric acid
• same mass / moles of metal
• same particle size of metal
• same temperature (of acid if comparing rate of bubbling)
Question 9 continued
AO /
Spec. Ref.
09.4 AO2
(203 × 30) + (205 × 70) 1 4.1.1.6
or
6090 + 14 350
= 204.4 ignore units 1
Total 11
How to answer it
Metals, Reactivity Series & Relative Atomic Mass
What this question tests
This question covers fundamental physical and chemical principles across GCSE Chemistry:
- Transition Metals (4.1.3): Contrasting typical transition element properties with Group 1 alkali metals.
- Displacement Reactions (4.4.1): Interpreting qualitative visual observations (solid deposition, colour changes) in terms of reactivity.
- Required Practical & Experimental Design (4.4.1 / RPA 4): Planning a fair comparison between metals and dilute acid to deduce relative reactivity.
- Isotopes & Relative Atomic Mass (4.1.1): Applying abundance ratios to calculate Ar accurately to a specified number of decimal places.
Transition Metal Properties
Identifying characteristic properties of transition elements
✅ Correct Answer (Tick 2 Boxes)
- ☑ They form ions with different charges. [1 mark]
- ☑ They have high melting points. [1 mark]
💡 Key Knowledge
Compare transition metals to Group 1 metals:
- Transition metals: high density, high melting point, hard/strong, form coloured compounds, catalytic activity, variable oxidation states (e.g. Fe²⁺ and Fe³⁺).
- Group 1 metals: soft, low density, low melting points, form white/colourless +1 compounds.
🧠 Exam Technique
Always count your ticks! The question specifies two boxes. If you tick more than two, examiners must subtract marks for incorrect extra selections.
❌ Common Errors
- Confusing transition metals with alkali metals (thinking they are soft or have low densities).
- Thinking transition compounds are colourless (e.g., Cu²⁺ salts are bright blue/green, not colourless).
Displacement in Solution: Copper & Silver Nitrate
Linking visual observations to chemical species and reactivity
✅ Model Answer
- The pale grey crystals are silver metal formed. [1 mark]
- The solution turns blue because copper ions (Cu²⁺) / copper nitrate are produced. [1 mark]
- This shows copper displaces silver because copper is more reactive than silver. [1 mark]
💡 Key Knowledge
The displacement equation is:
Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
- A more reactive metal displaces a less reactive metal from its salt solution.
- Aqueous Cu²⁺ ions give solutions a distinctive blue colour.
- Silver metal precipitating out of solution appears as grey/shiny needles.
🧠 Exam Technique
When asked how observations prove a rule, address both observations individually before stating the conclusion:
- Observation 1 (grey crystals) → What chemical is this?
- Observation 2 (blue colour) → What chemical caused this?
- Conclusion → What type of reaction happened?
❌ Common Errors
- Simply stating "copper is more reactive" without explaining what the crystals or blue colour actually are.
- Thinking the grey crystals are unreacted copper (copper is reddish-brown, not grey).
Planning an Investigation: Identifying Mg, Fe, and Cu
Designing a valid comparative method using dilute hydrochloric acid
✅ Model Plan (Full 4 Marks)
- Method: Measure a fixed volume of dilute hydrochloric acid into three separate boiling tubes / beakers.
- Control Variables: Keep acid volume, acid concentration, metal mass (or surface area), and starting temperature identical for each test.
- Measurements: Add each metal sample (X, Y, Z) separately and measure the temperature rise using a thermometer (or compare the rate of bubbling).
- Identification / Results:
- Copper: No reaction (no bubbles, no temperature change).
- Magnesium: Most reactive (fastest bubbling, largest temperature increase).
- Iron: Slower reaction than magnesium (slow bubbling, small temperature increase).
💡 Reactivity Order with Acid
Reactivity: Magnesium > Iron > [Hydrogen] > Copper
- Mg: Rapid effervescence; metal dissolves quickly; highly exothermic.
- Fe: Slow stream of bubbles; takes time to react; slight temperature change.
- Cu: Below hydrogen in the reactivity series → no reaction with dilute acid!
🧠 Level 2 Criteria (3–4 Marks)
To secure top marks on planning questions, you must provide:
- A clear outcome: How you will distinguish all three metals (not just one).
- Control variables: State at least two specific fair-test controls (e.g. same volume of acid, same mass/particle size).
- Logical order: Practical instructions in a clear, sensible sequence.
❌ Common Errors
- Forgetting to name control variables, limiting the response to Level 1 (max 2 marks).
- Claiming that copper fizzes slowly (copper does not react with dilute HCl).
- Saying "measure the reaction" without naming a measurable variable (e.g., temperature change or volume of gas).
Calculation: Relative Atomic Mass (Ar)
Calculating the weighted mean from percentage isotopic abundances
📐 Step-by-Step Calculation
- Multiply each mass by its percentage abundance:
(203 × 30) = 6090
(205 × 70) = 14350 - Sum the totals and divide by 100:
Ar = (6090 + 14350) / 100 [1 mark]
Ar = 20440 / 100 = 204.4 - Check decimal places:
The question demands 1 decimal place.
Final Answer = 204.4 [1 mark]
💡 Formula to Memorise
Ar = Σ (mass number × % abundance) / 100
Because 70% is 205 and only 30% is 203, the calculated average must lie closer to 205 than 203. Since 204.4 is between 203 and 205 and closer to 205, your sanity check passes!
❌ Common Calculation Traps
- Simple averaging: Doing (203 + 205) / 2 = 204 (ignores percentage abundance!).
- Rounding incorrectly: Writing 204 instead of following the instruction for 1 decimal place (204.4).
- Adding units: Relative atomic mass is a ratio and has no units (e.g. do not write 'g').
Topics
Chemistry · Required Practicals · C1: Atomic Structure and the Periodic Table · 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.