AQA GCSE Chemistry Chemistry Paper 1 (Higher), November 2021: Question 4
16 marks · Standard Demand difficulty · Short Answer
Explain the reactivity trends and reactions of Group 1 elements, including writing balanced equations, drawing dot and cross diagrams for sodium oxide, and explaining its high melting point.
Practise this questionQuestion
Question text
04 This question is about Group 1 elements.
04.1 Give two observations you could make when a small piece of potassium is added
to water.
[2 marks]
04.2 Complete the equation for the reaction of potassium with water.
You should balance the equation.
[2 marks]
K + H2O → +
04.3 Explain why the reactivity of elements changes going down Group 1.
[4 marks]
Sodium reacts with oxygen to produce the ionic compound sodium oxide.
Oxygen is a Group 6 element.
*0114.*4 Draw a dot and cross diagram to show what happens when atoms of sodium and
oxygen react to produce sodium oxide.
[4 marks]
Diagram
04.5 Why is oxygen described as being reduced in the reaction between sodium and
oxygen?
[1 mark]
04.6 Explain why sodium oxide has a high melting point.
[3 marks]
Mark scheme
Show the mark scheme
Question 4
AO /
Question Answers Extra information Mark
Spec. Ref.
04.1 any two from: 2 AO1
• (potassium) floats 4.1.2.5
• (potassium) melts 4.4.1.2
• (potassium) moves around
• potassium becomes smaller allow potassium disappears
• (lilac) flame
• effervescence allow fizzing
AO /
Spec. Ref.
04.2 2K + 2H2O → 2KOH + H2 allow multiples 2 AO1
AO2
allow 1 mark for KOH and H2 4.1.1.1
4.1.2.5
AO /
Spec. Ref.
04.3 reactivity increases (going down 1 AO1
the group) 4.1.2.5
4.4.1.2
(because) the outer electron / allow (because) there are more 1
shell is further from the nucleus shells
allow (because) the atoms get
larger
(so) there is less attraction allow (so) there is more 1
between the nucleus and the shielding from the nucleus
outer electron / shell
do not accept incorrect
attractions
– HEMISTRY – –
(so) the atom loses an electron 1
more easily
Question 4 continued
AO /
Spec. Ref.
04.4 allow use of outer shells only AO2
(dot and cross diagram to show) 4.2.1.1 13
sodium atom and oxygen atom 1 4.2.1.2
two sodium atoms to one allow two sodium ions to one 1
oxygen atom oxide ion
(to produce) sodium ion with a + 1
charge
(to produce) oxide ion with a 2– 1
charge
scores 4 marks – HEMISTRY – –
Question 4 continued
AO /
Spec. Ref.
04.5 (oxygen) gains electrons 1 AO1
14 4.4.1.4
AO /
Spec. Ref.
04.6 giant structure allow (giant ionic) lattice 1 AO1
4.2.1.3
4.2.2.1
(with) strong (electrostatic) 1 4.2.2.3
forces of attraction between
(oppositely charged) ions
(so) large amounts of energy allow (so) large amounts of 1
are needed to break the bonds / energy are needed to separate
forces the ions
Total 16
How to answer it
Group 1 Alkali Metals: Reactions, Periodic Trends & Ionic Bonding
Group 1 alkali metal chemistry, chemical equations, atomic structure explanations, ionic dot-and-cross representations, redox definitions, and lattice bonding properties:
- Observations: Recalling visible signs of reaction between potassium and water.
- Equations: Writing and balancing the reaction of an alkali metal with water.
- Periodic Trends: Explaining why reactivity increases down Group 1 using shielding, distance, and electrostatic attraction.
- Ionic Bonding: Drawing and describing electron transfer for Group 1 metal oxides ( Na₂O ).
- Redox: Defining reduction in terms of electron transfer (OIL RIG).
- Properties of Giant Structures: Explaining why ionic compounds have high melting points.
Observations of Potassium with Water
Visible changes when potassium reacts
✅ Correct Answers (Choose Any Two)
- (Lilac) flame
- Effervescence / fizzing / bubbles
- Potassium floats
- Potassium melts into a ball
- Potassium moves around on the surface
- Potassium gets smaller / disappears
🧠 Exam Technique: Observations vs Inferences
An observation is something you can directly see, hear, or feel.
- Say "fizzing" or "bubbles", not just "hydrogen is made".
- Say "lilac flame" (potassium produces a distinct lilac flame due to the heat igniting the hydrogen).
❌ Common Errors
- Stating chemical deductions such as "potassium hydroxide is formed" or "gas is produced" without describing the physical observation (fizzing).
- Giving an incorrect flame colour (e.g. yellow flame is sodium; brick-red is calcium).
Balancing the Chemical Equation
Reaction of potassium with water
✅ Balanced Chemical Equation
2K + 2H₂O → 2KOH + H₂
📐 Step-by-Step Balancing
- Identify products: Alkali metal + water → metal hydroxide + hydrogen gas:
K + H₂O → KOH + H₂ - Balance hydrogen: 2 H on left, 3 H on right. Put a 2 in front of H₂O and KOH:
K + 2H₂O → 2KOH + H₂ (4 H and 2 O on both sides). - Balance potassium: Put a 2 in front of K on the left:
2K + 2H₂O → 2KOH + H₂ .
❌ Common Errors
- Writing incorrect formulae for products like K₂O (potassium oxide) or KO instead of KOH .
- Writing hydrogen gas as monatomic H instead of diatomic H₂ .
Group 1 Reactivity Trend Explained
Why reactivity increases down Group 1
✅ Model 4-Mark Response
Reactivity increases going down Group 1 because:
- Trend stated: Reactivity increases down the group [1 mark].
- Atomic size: The atoms get larger / the outer electron is further away from the nucleus / there are more shells [1 mark].
- Attraction: There is less electrostatic attraction between the positive nucleus and the outer electron (due to greater distance and more shielding) [1 mark].
- Ease of loss: Therefore, the outer electron is lost more easily [1 mark].
💡 Key Knowledge: Cause and Effect Chain
Always structure Group 1 trend explanations in a 4-step logic chain:
Trend → Distance/Shells → Attraction/Shielding → Ease of electron loss.
❌ Common Errors
- Forgetting to explicitly state that reactivity increases.
- Confusing Group 1 with Group 7 (Group 7 reactivity decreases down the group because it gets harder to gain an electron).
- Saying the nucleus gets weaker. (The nuclear charge actually increases, but shielding and distance override it).
Dot and Cross Diagram: Sodium Oxide
Formation of an ionic compound ( Na₂O )
✅ Mark Scheme Criteria
- Correct electron structure of reactant atoms: two sodium atoms (each 2,8,1) and one oxygen atom (2,6) [1 mark].
- Correct ratio shown: two sodium atoms to one oxygen atom [1 mark].
- Sodium ions formed with a single positive charge: [Na]⁺ (electron configuration 2,8) [1 mark].
- Oxide ion formed with an eight-electron outer shell and 2- charge: [O]²⁻ (showing two dots/crosses transferred from sodium) [1 mark].
Reactants: Draw two separate Na atoms (each with 1 outer shell electron, e.g., dots •) and one Oxygen atom (with 6 outer shell electrons, e.g., crosses ×). Draw arrows showing one dot moving from each Na atom to complete the oxygen's shell.
Products: Draw two sodium ions in square brackets: [Na]⁺ (empty outer shell or 8 electrons) and one oxide ion in square brackets: [O]²⁻ with 6 crosses and 2 dots.
🧠 Exam Technique
The question allows showing outer shells only. This saves time and avoids mistakes in the inner shells. Always remember square brackets and correct charges ( + and 2- ).
❌ Common Errors
- Drawing covalent overlap sharing electrons instead of electron transfer into ions.
- Incorrect ratio (e.g. drawing 1 Na to 1 O, giving formula NaO instead of Na₂O).
- Forgetting brackets or omitting the charges on the ions.
Redox in Terms of Electrons
Why oxygen is reduced
✅ Correct Answer
Oxygen gains electrons.
💡 Key Knowledge: OIL RIG
- Oxidation Is Loss of electrons
- Reduction Is Gain of electrons
Each oxygen atom gains 2 electrons to form an oxide ion ( O²⁻ ).
❌ Common Errors
Defining reduction in terms of oxygen loss (e.g., "it loses oxygen"). Here oxygen is the element reacting, so the electron definition must be used!
Properties of Ionic Compounds: Melting Point
Explaining the high melting point of sodium oxide
✅ Model 3-Mark Response
- Sodium oxide has a giant structure / giant ionic lattice [1 mark].
- There are strong electrostatic forces of attraction between oppositely charged ions ( Na⁺ and O²⁻ ) [1 mark].
- Large amounts of energy are needed to break these strong bonds / overcome these forces [1 mark].
🧠 Exam Technique: Essential Buzzwords
To score all 3 marks on ionic melting point questions, you must hit all three key phrases:
- "Giant ionic lattice"
- "Strong electrostatic attraction between oppositely charged ions"
- "Large amount of energy required to overcome"
❌ Common Errors
- Referring to intermolecular forces or covalent bonds. Ionic substances have NO molecules and NO intermolecular forces!
- Mentioning "strong bonds" without specifying that they are between oppositely charged ions.
Topics
Chemistry · C1: Atomic Structure and the Periodic Table · C2: Bonding, Structure and the Properties of Matter · C4: Chemical Changes
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Higher), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.