AQA GCSE Chemistry Chemistry Paper 1 (Foundation), November 2020: Question 1
11 marks · Low Demand difficulty · Short Answer
Use data and trends of Group 7 elements to determine physical states, explain intermolecular forces, evaluate mass changes, predict reaction vigour, balance an equation, and calculate relative formula mass.
Practise this questionQuestion
Question text
01 This question is about the elements in Group 7 of the periodic table.
Table 1 shows the melting points and boiling points of some of the elements.
Table 1
Element Melting point in °C Boiling point in °C
Fluorine –220 –188
Chlorine –101 –35
Bromine –7 59
01.1 What is the state of bromine at 100 °C?
Use Table 1.
[1 mark]
Tick ( ) one box.
Gas
Liquid
Solid 3
01.2 What temperature does chlorine gas condense at to form a liquid?
Use Table 1.
[1 mark]
Temperature = °C
01.3 Complete the sentences.
[2 marks]
Going down Group 7 the melting points .
This is because the size of the molecules increases so the
intermolecular forces .
A teacher investigated the reaction of iron with chlorine.
*02* Figure 1 shows the apparatus used.
Figure 1
01.4 Why did the teacher do the investigation in a fume cupboard?
[1 mark]
Tick ( ) one box.
Chlorine gas is coloured.
Chlorine gas is flammable.
Chlorine gas is toxic. 5
01.5 The word equation for the reaction is:
iron + chlorine → iron chloride
Iron chloride is a solid.
The teacher weighed the glass tube and contents:
• before the reaction
• after the reaction.
What happened to the mass of the glass tube and contents during the reaction?
Give one reason for your answer.
[2 marks]
The mass of the glass tube and contents .
Reason
The teacher repeated the investigation with bromine gas and with iodine gas.
Table 2 shows the results.
Table 2
Element Observation
Chlorine Iron burns vigorously with an orange glow
Bromine Iron burns with an orange glow
Iodine Iron slowly turns darker
01.6 Fluorine is above chlorine in Group 7.
Predict what you would observe when fluorine gas reacts with iron.
Use Table 2.
[1 mark]
01.7 Balance the equation for the reaction between iron and bromine.
*05* [1 mark]
2Fe + … Br2 → 2FeBr3
01.8 Calculate the relative formula mass (Mr) of FeBr3
Relative atomic masses (Ar): Fe = 56 Br = 80
[2 marks]
Relative formula mass (Mr) =
Mark scheme
Show the mark scheme
Question 1
AO /
Question Answers Extra information Mark
Spec. Ref.
01.1 gas 1 AO2
4.1.2.6
4.2.2.1
01.2 -35 (°C) allow any value between -35 °C 1 AO2
and -100 °C 4.1.2.6
4.2.2.1
01.3 increase 1 AO1
AO2
increase allow become stronger 1 4.1.2.6
4.2.2.4
01.4 chlorine gas is toxic 1 AO3
4.1.2.6
01.5 increased 1 AO2
4.1.2.6
chlorine (atoms) are now part of 1 4.3.1.3
the solid (iron chloride)
or
the mass of the chlorine (atoms)
is now also measured
01.6 burns very vigorously allow burns violently 1 AO3
allow brighter (orange) glow 4.1.2.1
allow (orange) flame 4.1.2.6
allow explodes
Question 1 continued
AO /
Spec. Ref.
01.7 2 Fe + 3 Br2 → 2 FeBr3 allow multiples 1 AO2
4.1.1.1
4.1.2.6
01.8 56 + (3 × 80) 1 AO2
4.3.1.2
= 296 ignore units 1
Total 11
How to answer it
Group 7 Halogens: Physical Trends, Reactions & Formula Mass
This 11-mark foundational question assesses your understanding of the Group 7 elements (halogens). Specifically:
- Physical States & Phase Changes: Deducing states of matter from melting and boiling points.
- Group Trends & Bonding: Explaining melting point trends in terms of molecular size and intermolecular forces.
- Lab Safety & Hazards: Recognising toxicity of chlorine gas.
- Conservation of Mass: Explaining apparent mass changes when a gas reacts to form a solid.
- Reactivity Trends: Predicting halogen reactivity going up the group.
- Quantitative Chemistry: Balancing chemical equations and calculating relative formula mass (Mr).
State of Bromine at 100 °C
Deducing states of matter from melting and boiling points
✅ Correct Answer
Tick: Gas
💡 Key Knowledge
Look at Table 1 for Bromine:
- Melting point = -7 °C
- Boiling point = 59 °C
- If temperature < melting point → Solid
- If temperature is between MP and BP → Liquid
- If temperature > boiling point → Gas
Since 100 °C is greater than 59 °C, bromine must be a gas.
Condensation Temperature of Chlorine
Linking state changes to boiling point
✅ Correct Answer
Temperature = -35 °C
🧠 Exam Technique
Condensation is the exact reverse of boiling. Therefore, a substance condenses at its boiling point.
For chlorine, boiling point = -35 °C.
❌ Common Errors
Confusing condensing with freezing. Freezing occurs at the melting point (-101 °C), while condensation occurs at the boiling point (-35 °C).
Trend in Melting Points Down Group 7
Explaining physical properties using intermolecular forces
✅ Correct Answer
Going down Group 7 the melting points increase. [1]
This is because the size of the molecules increases so the intermolecular forces increase (or become stronger). [1]
💡 Key Knowledge
- Group 7 elements exist as diatomic molecules (e.g. F₂, Cl₂, Br₂, I₂).
- As you go down the group, atoms get larger → molecules become bigger → intermolecular forces increase in strength.
- Stronger intermolecular forces require more energy to overcome, so melting and boiling points increase.
❌ Common Errors
Never say "covalent bonds get stronger" or "covalent bonds break"! Covalent bonds inside the molecules do not break when halogens melt or boil; only weak intermolecular forces between molecules are overcome.
Safety in the Laboratory: Fume Cupboards
Chemical hazard identification
✅ Correct Answer
Tick: Chlorine gas is toxic.
💡 Key Knowledge
A fume cupboard is used whenever harmful, irritating, or poisonous/toxic gases are produced or used in an experiment to prevent inhalation.
Chlorine is a toxic green gas; it is not flammable.
Mass Change During the Reaction
Apparent mass changes in open systems & conservation of mass
✅ Correct Answer
The mass of the glass tube and contents increased. [1]
Reason: Chlorine (atoms) are now part of the solid (iron chloride) / the mass of the chlorine that reacted is now also measured. [1]
🧠 Exam Technique
Before the reaction, only the iron was weighed inside the tube. During the reaction, chlorine gas from the supply combined with the iron to make solid iron chloride ( 2Fe + 3Cl₂ → 2FeCl₃ ). Because gaseous chlorine atoms bonded to the iron and remained inside the tube as a solid, the recorded mass increased!
❌ Common Errors
Saying mass "stayed the same because of conservation of mass". Total mass in the universe is conserved, but the question asks about the contents of the tube. A gas entered and was captured into a solid, so the tube's contents gained mass.
Predicting Reactivity: Fluorine and Iron
Extrapolating trends in Group 7 reactivity
✅ Correct Answer
Accept any of the following:
- Burns very vigorously
- Burns violently / explodes
- Brighter (orange) glow / (orange) flame
💡 Key Knowledge
Look at the trend down Group 7 in Table 2:
- Chlorine: Burns vigorously with an orange glow
- Bromine: Burns with an orange glow
- Iodine: Slowly turns darker
Reactivity decreases down Group 7. Fluorine is above chlorine, so it must be the most reactive.
Balancing the Chemical Equation
Balancing halogen molecules
✅ Correct Answer
2Fe + 3 Br₂ → 2FeBr₃
📐 Balancing Step-by-Step
- Look at the product side: 2FeBr₃ contains 2 × 3 = 6 bromine atoms.
- Look at the reactant side: bromine comes as diatomic molecules ( Br₂ ).
- To get 6 Br atoms from Br₂: 6 ÷ 2 = 3.
Relative Formula Mass (Mr) of FeBr₃
Calculating relative formula mass from relative atomic masses (Ar)
📐 Step-by-Step Calculation
Given: Ar of Fe = 56, Ar of Br = 80
- Identify number of each atom in FeBr₃:
1 × Fe atom, 3 × Br atoms - Substitute atomic masses:
Mr = 56 + (3 × 80) [1 mark] - Calculate total:
Mr = 56 + 240 = 296 [1 mark]
❌ Common Errors
- Multiplying the whole mass by 3: (56 + 80) × 3 = 408 ✗
- Forgetting that there are 3 bromines: 56 + 80 = 136 ✗
- Always check the subscript numbers in chemical formulas: the subscript 3 belongs only to Br!
Topics
Chemistry · C1: Atomic Structure and the Periodic Table · C2: Bonding, Structure and the Properties of Matter · C3: Quantitative Chemistry
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.