Edexcel A-Level Chemistry AS Paper 1, June 2023: Question 4

7 marks · Medium difficulty · Calculations

Explain the high melting temperature of magnesium due to its structure, calculate the minimum volume of hydrochloric acid required to react with potassium manganate(VII) to produce a given mass of magnesium chloride, and identify the meaning of a hazard symbol.

Practise this question

Question

Diagram showing an apparatus setup where concentrated hydrochloric acid is added from a dropping funnel into a conical flask containing potassium manganate(VII) to generate chlorine gas, which passes over a coil of magnesium ribbon inside a heated tube. Part (a) asks to explain why the structure of magnesium gives it a high melting temperature. Part (b) provides equations for the reaction to produce chlorine and the reaction between chlorine and magnesium, asking to calculate the minimum volume of hydrochloric acid in cm3 required to produce 4.00 g of magnesium chloride. Part (c) shows a diamond-shaped hazard symbol depicting a flame over a circle (oxidising agent) and asks multiple-choice options about what this hazard symbol means.

Question text

4 The reaction between magnesium and chlorine can be carried out using the

apparatus shown.

concentrated tube containing coil of

hydrochloric acid magnesium ribbon

(11.5 mol dm–3) hole

flask containing

potassium manganate(VII)

The coil of magnesium ribbon is first heated strongly until it just melts.

Chlorine gas is then produced by a chemical reaction in the conical flask.

The chlorine gas is passed over the heated magnesium, resulting in the formation of

magnesium chloride.

(a) In order to melt the magnesium, it must be heated strongly.

Explain why the structure of magnesium gives it a high melting temperature.

(2)

(b) The equation for the reaction to produce chlorine is shown.

2KMnO4 + 8HCl → 3Cl2 + 2KCl + 2MnO2 + 4H2O

The concentration of the hydrochloric acid is 11.5 mol dm–3.

The equation for the reaction between the chlorine and the magnesium is shown.

Mg + Cl2 → MgCl2

Calculate the minimum volume of concentrated hydrochloric acid, in*P71926A0928* cm3,

required to produce 4.00g of magnesium chloride, MgCl2.

Give your answer to an appropriate number of significant figures.

(4)

One of these is shown.

This hazard symbol means that potassium manganate(VII) is liable to

(1)

A burn easily in the presence of oxygen

B explode

C react dangerously with oxygen

D react vigorously with reducing agents

(Total for Question 4 = 7 marks)

Mark scheme

Show the mark scheme

Question Answer Additional Guidance Mark

Number

4(a) An answer that makes reference to the following (2)

points:

• giant metallic structure / giant lattice (1) Allow just lattice structure

structure Allow large instead of giant

Allow giant crystal structure

Allow many ions and a sea of / many delocalised electrons

Do not award just metallic structure

Do not award giant covalent lattice

Do not award giant ionic lattice

• strong (electrostatic) attraction between Ignore references to energy

metal ions / positive ions / cations and Allow electrons moving / free to move within the metal for the

delocalised electrons (1) delocalised electrons

May be shown on a labelled diagram

Number

4(b) Example of calculation: (4)

• calculation of moles of magnesium chloride (1) 4.00 = 0.041973 (ans 1)

95.3

Do not award = 0.04

• (calculation of moles of chlorine gas (moles of Cl2 : moles of MgCl2 = 1:1

required) moles of Cl2 = (ans 1) = 0.041973 (ans 2)

and and

calculation of moles of HCl required (1) moles of HCl : moles of Cl2 = 8:3

moles of HCl = 8÷3 x (ans 2) = 0.11193 (ans 3)

• calculation of volume of hydrochloric acid (1) volume = moles/concentration = (ans 3)÷11.5

volume = 0.0097328 (dm3) / 9.7328 (cm3)

39.8 (cm3)

• answer in cm and to 2 SF or 3SF with one

decimal place (1) Allow 9.7 / 10 / 10.0

Allow TE throughout

Question

Answer Mark

Number

4(c) (1)

The only correct answer is D (react vigorously with reducing agents)

A is not correct because the symbol shown is for oxidising agents, not flammable

B is not correct because the symbol shown is for oxidising agents not explosive

C is not correct because the symbol given is for oxidising agents which do not usually react dangerously with oxygen

(Total for Question 4 = 7 marks)

How to answer it

Preparation of Chlorine & Properties of Magnesium

What this question tests

This question assesses metallic bonding and melting temperatures, multi-step stoichiometry calculations involving reacting mole ratios and solution concentrations, and the interpretation of standard hazard warning symbols.

Question 4(a)

Melting Temperature of Magnesium

Explain why the structure of magnesium gives it a high melting temperature. (2 marks)

✅ Correct Answer

Magnesium has a giant metallic structure / giant lattice structure. (1 mark)
There is a strong electrostatic attraction between positive metal ions (cations) and delocalised electrons. (1 mark)

❌ Common Errors

Saying just "metallic bonding" without mentioning the giant structure.
Incorrectly referring to a "giant covalent" or "giant ionic" lattice.
Forgetting to state that the electrostatic attraction is strong.

Mark scheme guidance: "Giant lattice structure" or "giant metallic structure" is essential for the first mark. Mentioning strong electrostatic attraction between positive ions and delocalised electrons secures the second.

Question 4(b)

Stoichiometry & Solution Calculations

Calculate the minimum volume of concentrated hydrochloric acid, in cm³, required to produce 4.00 g of magnesium chloride. Give your answer to an appropriate number of significant figures. (4 marks)

📐 Step-by-Step Calculation

Moles of MgCl₂:
Molar mass of MgCl₂ = 24.3 + (2 × 35.5) = 95.3 g mol⁻¹
Moles = 4.00 / 95.3 = 0.041973 mol
Moles of Cl₂ and HCl required:
From Mg + Cl₂ → MgCl₂ , mole ratio MgCl₂ : Cl₂ is 1 : 1. So moles of Cl₂ = 0.041973 mol
From 2KMnO₄ + 8HCl → 3Cl₂... , mole ratio Cl₂ : HCl is 3 : 8.
Moles of HCl = 0.041973 × (8 / 3) = 0.11193 mol
Volume of HCl solution:
Volume (dm³) = Moles / Concentration = 0.11193 / 11.5 = 0.0097328 dm³
Volume (cm³) = 0.0097328 × 1000 = 9.7328 cm³
Final Answer & Sig Figs:
= 9.8 cm³ (to 2 significant figures, matching the 4.00 g data given in the question).

🧠 Exam Technique & Traps

The 3:8 Ratio Trap: A very common error is misreading or incorrectly inverting the stoichiometric ratio from the complex equation containing KMnO₄ and HCl. Always use 8/3 , not 3/8 .
Significant Figures: The input data 4.00 g is given to 3 SF, but input concentration 11.5 mol dm⁻³ is to 3 SF. Giving an answer to 2 SF ( 9.8 cm³ ) or 3 SF ( 9.73 cm³ ) is accepted by the mark scheme. Avoid rounding intermediate steps too early!
Units: Do not forget to multiply by 1000 to convert dm³ into cm³.

Question 4(c)

Hazard Warning Symbols

This hazard symbol means that potassium manganate(VII) is liable to... (1 mark)

✅ Correct Answer

D: react vigorously with reducing agents

The symbol depicted is the flame over a circle, which denotes an oxidising agent.
Oxidising agents accept electrons and react vigorously with reducing agents.

💡 Why other options are wrong

A: The symbol for flammable/burns easily is just a standalone flame (without the circle).
B: The symbol for explosive is an exploding bomb.
C: Oxygen gas itself is not the reactant being described by this specific reactivity hazard category in this context.

Topics

Physical Chemistry · Inorganic Chemistry · Topic 2: Bonding and Structure · Topic 5: Formulae, Equations and Amounts of Substance · Topic 3: Redox I

Question and mark scheme from the Edexcel A-Level Chemistry examination, AS Paper 1, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.