4ch1-2c-que-20231121

Question 1

This question is about Group 7, the halogens.

(a) What is the total number of electrons in one fluorine atom?

A) 7
B) 9
C) 10
D) 19

(b) What is the charge on a bromide ion?

A) \(1-\)
B) \(1+\)
C) \(2-\)
D) \(2+\)

(c) Which of these describes the element iodine at room temperature?

A) brown liquid
B) brown solid
C) grey solid
D) purple gas

(d) When a halogen is added to a solution containing halide ions, a displacement reaction may occur.

The table shows whether a reaction occurs.

Halogen added	Chloride ion in solution	Bromide ion in solution	Iodide ion in solution
chlorine		reaction	reaction
bromine	no reaction		reaction
iodine	no reaction	no reaction

Using information from the table, explain the order of reactivity of the three halogens.

Most-appropriate topic codes (Edexcel IGCSE Chemistry):

• 1(d): The Periodic Table — parts (a), (b), (c) – atomic number, ion charges, physical states
• 2(b): Group 7 (halogens) – chlorine, bromine and iodine — parts (a), (b), (c), (d) – properties, reactivity trends, displacement reactions
• 2.5: Know the colours, physical states (at room temperature) and trends in physical properties — part (c)
• 2.7: Understand how displacement reactions involving halogens and halides provide evidence for the trend in reactivity in Group 7 — part (d)

▶️ Answer/Explanation

Solution

(a) B (9)
A is incorrect as there are not 7 electrons in total
C is incorrect as there are not 10 electrons in total
D is incorrect as there are not 19 electrons in total

(b) A (\(1-\))
B is incorrect as the charge on a bromide ion is not \(1+\)
C is incorrect as the charge on a bromide ion is not \(2-\)
D is incorrect as the charge on a bromide ion is not \(2+\)

(c) C (grey solid)
A is not correct as iodine is not a brown liquid at room temperature
B is not correct as iodine is not a brown solid at room temperature
D is not correct as iodine is not a purple gas at room temperature

(d) An explanation that links the following three points:
• chlorine displaces bromine and iodine/chlorine reacts with bromide and iodide (ions)
• bromine displaces iodine/iodine doesn’t displace chlorine or bromine/bromine reacts with iodide (ions)/iodine doesn’t react with chloride or bromide (ions)
• most reactive chlorine, then bromine, least reactive iodine
Allow: “chlorine is most reactive and iodine is least reactive” or “reactivity decreases down the group”.

Total marks: 6

Question 2

This question is about gases in the atmosphere.

A teacher uses this apparatus to determine the percentage of oxygen in air.

The teacher removes the stopper, ignites the magnesium ribbon and immediately replaces the stopper. The magnesium reacts with oxygen to form magnesium oxide. During the reaction the water level in the bell jar rises. When the flame goes out, some magnesium remains in the basin.

(a) (i) Give the appearance of the magnesium oxide.
(ii) Give a chemical equation for the reaction of magnesium with oxygen.
(iii) Explain why the water in the bell jar rises.

(b) The volume of air in the bell jar at the start of the reaction is \(2000 \, \text{cm}^3\). When the reaction ends, the apparatus cools down to room temperature. Calculate the expected volume of gas in the bell jar at room temperature.

(c) State why the gas remaining in the bell jar at the end of the reaction is approximately 99% nitrogen.

Most-appropriate topic codes (Edexcel IGCSE Chemistry 4CH1):

• 2(c): Gases in the atmosphere — all parts
• 1(e): Chemical formulae, equations and calculations — parts (a)(ii), (b)
• 1(a): States of matter — part (a)(iii)

▶️ Answer/Explanation

Solution

(a)(i) white solid/powder/ash
ALLOW (pale/light) grey solid/powder /ash
REJECT white precipitate

(a)(ii) \( 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \)
ALLOW multiples and fractions.
IGNORE state symbols even if incorrect.

(a)(iii) An explanation that links the following two points:
M1: (Oxygen is used in the reaction so) volume/amount of air/oxygen decreases / pressure decreases.
M2: (Water level rises) to take the place of the oxygen / to equalise the pressure OWTTE.
ALLOW arguments in terms of pressure.

(b)
M1: percentage of oxygen in air = 21% / percentage of air remaining = 79%
ALLOW 20% / 80%
M2: volume of air remaining = \( 2000 \times \frac{79}{100} \)
M2 subsumes M1. ALLOW ecf if incorrect percentage used.
M3: \( 1580 \, \text{cm}^3 \)
Use of 80% gives an answer of \(1600 \, \text{cm}^3\).
Correct answer of 1580 or 1600 without working scores 3.
420 /400 scores 2.

(c) The percentages of argon and carbon dioxide are very small OWTTE.
ACCEPT references to approximate percentages.
ALLOW (all the oxygen has been removed and) only 1% / small amounts of the other gases remain.

Question 3

This question is about aluminium.

(a) State why aluminium cannot be extracted by heating aluminium oxide with carbon.

(b) Aluminium is a metal with many uses.

Aluminium is malleable, a good conductor of heat and electricity, and has a low density compared to most other metals.

Explain two uses of aluminium that are related to its properties.

(c) The diagram represents the structure of pure aluminium, and the structure of an alloy of aluminium.

Use the diagram to explain why the alloy is harder than pure aluminium.

Most-appropriate topic codes (Edexcel IGCSE Chemistry):

• 2(e): Extraction and uses of metals — part (a)
• 2(e): Extraction and uses of metals — part (b)
• 1(h): Metallic bonding — part (c)
• 2(e): Extraction and uses of metals (Alloys) — part (c)

▶️ Answer/Explanation

Mark Scheme

(a)

Question number	Answer	Notes	Marks
3 (a)	aluminium/it is more reactive than carbon / aluminium/it is above carbon in the reactivity series ORA		1

(b)

An explanation which links two pairs of points (In all cases M2 is dependent on M1)

Pair	M1 (Use)	M2 (Related Property)	Notes
1	drink cans	malleable / low density	ALLOW does not corrode / non-toxic / doesn’t react with the drink
2	aircraft / aeroplanes / bicycle frames / car bodies	low density	ALLOW does not corrode
3	(overhead) power cables / wires	(good) conductor of electricity / low density / malleable / ductile
4	pans	(good) conductor of heat	ALLOW does not corrode / non-toxic / doesn’t react with the food
5	(aluminium) foil	malleable	ALLOW does not corrode / non-toxic / doesn’t react with the food / prevents heat loss

ACCEPT any correct use with corresponding relevant property. REJECT any incorrect answer for M2. (Total 4 marks for part b)

(c)

An explanation that links the following three points:

M1: in pure metal layers (of atoms/cations/particles) slide over each other (easily) OWTTE.
M2: in an alloy the different sized/larger atoms/cations/particles disrupt the structure/are more randomly arranged.
M3: which prevents layers (of atoms/cations/particles) sliding over each other.

ALLOW sheets/rows for layers. REJECT molecules / intermolecular forces / negative ions / anions / ionic / covalent for 1 mark only. Deduct 1 mark if no mention of layers/sheets/rows. (Total 3 marks for part c)

Total for Question 3: 8 marks

Question 4

A student uses this method to investigate the reaction between sodium hydroxide solution and dilute hydrochloric acid.

pour 25 cm³ of dilute hydrochloric acid into a glass beaker
measure the temperature of the acid
add 5 cm³ of sodium hydroxide solution and stir the mixture
record the highest temperature reached
continue to add further 5 cm³ portions of sodium hydroxide solution until a total of 40 cm³ has been added
record the temperature after adding each 5 cm³ portion of sodium hydroxide solution

(a) State two factors that the student must keep constant to make this a valid investigation.

(b) Explain how using a polystyrene cup, instead of a glass beaker, would increase the accuracy of the results.

(c) The graph shows the student’s results.

(i) Use the graph to determine the maximum temperature change in °C.
(ii) Explain the shape of the graph.

(d) The student repeats the experiment using a polystyrene cup. These are the student’s results.

Maximum temperature change	35 °C
Volume of hydrochloric acid	25 cm³
Volume of sodium hydroxide solution added for complete reaction	22 cm³

Calculate the heat energy change (\(Q\)) in kJ.
[for the solution, 1.0 cm³ has a mass of 1.0 g \(c = 4.2 \text{ J g}^{-1} \text{ °C}^{-1}\)]

Most-appropriate topic codes (Edexcel IGCSE Chemistry 4CH1):

• 3(a) Energetics — parts (c), (d)
• 2(g) Acids, bases and salt preparations / 2(f) Acids, alkalis and titrations — context of neutralisation
• 3(a) Assessment of experimental methods — parts (a), (b)
• Specification Point 3.3: calculate the heat energy change from a measured temperature change using the expression \(Q = mc\Delta T\) — part (d)
• Specification Point 3.8: practical: investigate temperature changes accompanying some of the following types of change: … neutralisation reactions — whole investigation

▶️ Answer/Explanation

Solution

(a) Any two from:

concentration of sodium hydroxide (solution)
rate of / same stirring
temperature of sodium hydroxide (solution) / temperature of the room

(IGNORE references to concentration of acid. IGNORE references to volume / mass / amount of either solution.)

(b) An explanation that links any two of the following points:

polystyrene/it is a better insulator than glass / it is an insulator
less heat/thermal energy will be lost / it prevents heat loss
using a polystyrene cup will lead to a more accurate/a higher temperature (change)

(c)(i) any value between 32.0 and 33.0 inclusive (e.g., 32.5 °C)

(c)(ii) An explanation that links the following three points:

The first line shows that as more sodium hydroxide is added the temperature rises (at a steady rate) / the temperature is directly proportional to the volume added.
The point where the lines cross / the highest temperature reached / the volume of 21–22 cm³ of sodium hydroxide shows that the sodium hydroxide has neutralised the acid / the acid has fully reacted.
The second line shows that (there is no further reaction and) the cool sodium hydroxide solution decreases the temperature / the mixture cools down.

(d)

M1: mass of solution = \(25 + 22 = 47 \text{ g}\)

M2: \(Q = mc\Delta T\)

M3: \(Q = 47 \times 4.2 \times 35 = 6909 \text{ J}\)

M4: \(6909 \text{ J} = 6.909 \text{ kJ} \approx 6.9 \text{ kJ}\) (accept any number of significant figures correctly rounded except 1)

Correct answer without working scores full marks. ALLOW ecf (error carried forward) from an incorrect mass in M1.

Question 5

This question is about carboxylic acids and esters.

(a) Ethanoic acid reacts with magnesium to form two products.

(i) Complete the equation for this reaction.

\(……… + ……… \to (CH_{3}COO)_{2}Mg + ………\)

(ii) Give two observations that could be made during this reaction.

(b) Propanoic acid reacts with methanol to form an ester.

(i) Give the name of a suitable catalyst for this reaction.

(ii) What is the structural formula of the ester that forms?

A) \(\text{HCOOCH}_2\text{CH}_2\text{CH}_3\)
B) \(\text{CH}_3\text{COOCH}_2\text{CH}_2\text{CH}_3\)
C) \(\text{CH}_3\text{CH}_2\text{COOCH}_3\)
D) \(\text{CH}_3\text{CH}_2\text{CH}_2\text{COOCH}_3\)

(c) A polyester can be made by reacting ethanedioic acid with ethanediol.
These are the displayed formulae of the two reactants.

(i) Give the name for this type of polymerisation.
(ii) Give the name of the other product of this reaction.
(iii) Draw the displayed formula for the repeat unit of the polyester that forms.

(d) State what is meant by the term biopolyester.

Most-appropriate topic codes (Edexcel IGCSE Chemistry):

• 4(f): Carboxylic acids — part (a)
• 4(g): Esters — parts (b), (c)(i), (c)(ii), (c)(iii)
• 4(h): Synthetic polymers — parts (c)(i), (c)(ii), (c)(iii), (d)

▶️ Answer/Explanation

Solution

(a)(i) \(2\text{CH}_3\text{COOH} + \text{Mg} \rightarrow (\text{CH}_3\text{COO})_2\text{Mg} + \text{H}_2\)

Notes: Multiples and fractions are acceptable. State symbols are ignored even if incorrect.

(a)(ii)
1. Effervescence / fizzing / bubbles.
2. Magnesium becomes smaller / disappears / dissolves.

(b)(i) Concentrated sulfuric acid.

Note: Any suitable inorganic acid (e.g., hydrochloric, nitric, phosphoric) is acceptable. “Dilute” is ignored.

(b)(ii) C (\( \text{CH}_3\text{CH}_2\text{COOCH}_3 \))
Explanation:
• A is incorrect; it is propyl methanoate.
• B is incorrect; it is propyl ethanoate.
• D is incorrect; it is methyl butanoate.

(c)(i) Condensation polymerisation.

(c)(ii) Water.

(c)(iii)

(d) A polyester that is biodegradable / can be degraded by bacteria / can be decomposed.

Question 6

(a) The diagram shows two pieces of apparatus used in a titration.

Give the names of these pieces of apparatus.

(b) Give the name of a suitable indicator that can be used in an acid-alkali titration.

(c) A student does a titration using sodium carbonate solution and dilute nitric acid.

This is the equation for the reaction:

\[ \text{Na}_2\text{CO}_3 + 2\text{HNO}_3 \rightarrow 2\text{NaNO}_3 + \text{CO}_2 + \text{H}_2\text{O} \]

The table shows the concentrations of the two solutions and the volume of sodium carbonate used in the titration.

Concentration of nitric acid in mol/dm\(^3\)	0.350
Concentration of sodium carbonate solution in mol/dm\(^3\)	0.220
Volume of sodium carbonate solution in cm\(^3\)	25.0

Use the equation and the data in the table to answer these questions.

(i) Calculate the volume of dilute nitric acid that the student would need to neutralise the sodium carbonate solution.

(ii) Calculate the volume, in cm\(^3\), of carbon dioxide gas at rtp that would be produced from the 25.0 cm\(^3\) of the sodium carbonate solution.
[at rtp, molar volume = 24 000 cm\(^3\)]

(d) Describe a test to show that sodium carbonate solution contains carbonate ions.

Most-appropriate topic codes (Edexcel IGCSE Chemistry – 4CH1):

• 2(f): Acids, alkalis and titrations — part (a), (b)
• 1(e): Chemical formulae, equations and calculations — part (c)(i), (c)(ii)
• 1(e) 1.35C: Calculations involving gas volumes and molar volume — part (c)(ii)
• 2(h): Chemical tests — part (d)
• 2(g): Acids, bases and salt preparations — part (c), (d)

▶️ Answer/Explanation

Solution

(a)

M1 (X) pipette
M2 (Y) burette

(b) methyl orange / phenolphthalein / litmus (solution)

REJECT universal indicator, litmus paper. ACCEPT other appropriate indicators.

(c) (i)

M1 (moles of Na\(_2\)CO\(_3\) =) \(0.220 \times \frac{25.0}{1000} = 0.00550\) mol
M2 From equation: Na\(_2\)CO\(_3\) : HNO\(_3\) = 1 : 2
moles of HNO\(_3\) = \(0.00550 \times 2 = 0.0110\) mol
M3 Volume of HNO\(_3\) = \(\frac{0.0110}{0.350} \times 1000 = 31.4\) cm\(^3\)

volume of nitric acid = 31.4 cm\(^3\)

(c) (ii)

M1 From equation: Na\(_2\)CO\(_3\) : CO\(_2\) = 1 : 1
moles of CO\(_2\) = 0.00550 mol
M2 Volume of CO\(_2\) at rtp = \(0.00550 \times 24\,000 = 132\) cm\(^3\)

volume of carbon dioxide = 132 cm\(^3\)

(d)

A description that refers to the following three points:

M1 Add (dilute) hydrochloric acid (to the sodium carbonate solution)
ALLOW any suitable named acid.
M2 Bubble/pass the gas through limewater OR test the gas with limewater
M2 dependent on M1 or mention of adding acid.
M3 (Limewater) turns milky/cloudy
ALLOW white precipitate. M3 dependent on limewater.

Question 7

(a) Sodium chloride is an ionic compound.

Explain why sodium chloride conducts electricity when it is molten or in solution, but not when it is solid.

(b) A solution of sodium chloride can be electrolysed using this apparatus.

(i) If the solution is dilute, a significant amount of oxygen collects at P.

Complete the ionic half-equation for this reaction.

\( …….. H_{2}O\to ……..H^{+} + …….. O_{2}+ ……..e^{-}\)

(ii) If the solution is concentrated, chlorine is the main product that collects at P.

This is the ionic half-equation for the reaction.

\[ 2Cl^- \rightarrow Cl_2 + 2e^- \]

State why this is an oxidation reaction.

(c) The gas that collects at Q is hydrogen.

(i) Give a test for hydrogen.
(ii) Explain how hydrogen gas forms at the negative electrode.

(d) Hydrogen reacts with oxygen to form water.

The equation shows the covalent bonds in the molecules.

\[ 2H-H + O=O \rightarrow 2H-O-H \]

The table gives the bond energies.

Bond	\( H-H \)	\( O=O \)	\( O-H \)
Bond energy in kJ/mol	436	498	463

(i) Use the equation and the values in the table to calculate the enthalpy change, \(\Delta H\), for the reaction. Include a sign in your answer.

(ii) Complete the diagram to show the energy levels of the reactants and products, and the enthalpy change, \(\Delta H\).

Most-appropriate topic codes (Edexcel IGCSE Chemistry):

• 1(f) & 1(i): Ionic bonding & Electrolysis — parts (a), (b), (c)(ii)
• 1(i) Electrolysis: — parts (b)(i), (b)(ii), (c)(i), (c)(ii)
• 3(a) Energetics: — parts (d)(i), (d)(ii)
• 2(h) Chemical tests: — part (c)(i)

▶️ Answer/Explanation

Solution

(a)

An explanation that links the two points:
M1 In solid sodium chloride ions are in a fixed position/in a lattice/cannot move.
M2 When molten or in solution ions are free to move/flow.

(b)(i)

\[ 2H_2O \rightarrow 4H^+ + (1)O_2 + 4e^- \]

(b)(ii)

Chloride (ions)/(2)Cl⁻/it lose electrons.

(c)(i)

(Squeaky) pop with lighted splint.

(c)(ii)

An explanation that links any three of the following four points:
M1 Solution/water contains hydrogen ions/H⁺.
M2 Hydrogen ions/H⁺ are attracted to the negative electrode/cathode.
M3 Hydrogen ions/H⁺ gain electrons.
M4 And (combine in pairs to) form hydrogen molecules/H₂.

(d)(i)

M1 \(\sum\) bond energies on LHS = \(2 \times 436 + 498 = 1370\) kJ
M2 \(\sum\) bond energies on RHS = \(4 \times 463 = 1852\) kJ
M3 \(1370 – 1852 = -482\) kJ

\[ \Delta H = -482 \text{ kJ} \]

d)(ii)

Diagram showing:
M1 Two horizontal lines in correct positions with products line to the right of reactants line.
M2 Horizontal lines labelled correctly with formulae of reactants (\(2H_2 + O_2\)) and products (\(2H_2O\)).
M3 Vertical line in correct position and labelled \(\Delta H\).

Correct energy profile diagram for an exothermic reaction.

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