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Paper 4 style practice paper: Theory (Extended) — mark scheme

QuizQuipPractice Series
QQ/IGCSE-CHEM/P4S

IGCSE · Cambridge IGCSE Chemistry (Extended)

Mark scheme

Theory (Extended)

Paper 4 style practice paper · Maximum mark: 40

Notes for markers

  • Award one mark for each point marked [1], up to the marks shown for the part.
  • Accept answers worded differently that show the same understanding.
  • Units are required where the answer line shows one. ecf: allow an error carried forward.

Section A: Structured questions[20 marks]

QuestionAnswer and marking pointsMarks
1(a)

13 electrons.

  • 13 electrons (same as the number of protons) [1]
1
1(b)

27 (13 protons + 14 neutrons). [1]

1
1(c)

They have the same number of electrons in their outer shell, so their chemical properties are the same.

  • same number of outer-shell electrons / same electronic configuration [1]
1
Total for Question 13
2(a)

4.8 ÷ 24 = 0.20 mol. [1]

1
2(b)

The ratio of Mg to MgO is 2 : 2, so 0.20 mol of magnesium oxide forms.

  • 0.20 mol (1 : 1 ratio) [1]
1
2(c)

Mᵣ of MgO = 24 + 16 = 40, so mass = 0.20 × 40 = 8.0 g.

  • Mᵣ of MgO = 40 [1]
  • mass = 0.20 × 40 = 8.0 g [1]
2
2(d)

0.10 mol of oxygen is used, so the volume is 0.10 × 24 = 2.4 dm³. [1]

1
Total for Question 25
3(a)

hydrogen [1]

1
3(b)

Hold a lighted splint to the gas; it burns with a squeaky pop.

  • lighted splint gives a squeaky pop [1]
1
3(c)

Sodium is more reactive than hydrogen, so the sodium ions stay in solution and the hydrogen ions gain electrons at the cathode instead.

  • sodium ions remain in solution / sodium is more reactive than hydrogen [1]
  • hydrogen ions gain electrons at the cathode [1]
2
Total for Question 34
4(a)

endothermic [1]

1
4(b)

The process takes in energy from the water, so the water loses energy and its temperature falls.

  • energy is taken in from the surroundings (the water) [1]
  • the water loses energy, so its temperature falls [1]
2
4(c)

Any one of: burning a fuel; neutralising an acid with an alkali; adding water to calcium oxide.

  • burning / neutralisation / reaction of calcium oxide with water [1]
1
Total for Question 44
5(a)

Neutralisation.

  • neutralisation / acid–base reaction [1]
1
5(b)

So that all of the acid has reacted and the acid is not in excess.

  • all the acid is used up / acid is not in excess [1]
1
5(c)

Filter the mixture. The unreacted copper(II) oxide stays on the filter paper as the residue, and the copper(II) sulfate solution passes through as the filtrate.

  • filter the mixture [1]
  • copper(II) oxide remains as the residue / solid on the filter paper [1]
2
Total for Question 54

Section B: Structured questions[20 marks]

QuestionAnswer and marking pointsMarks
6(a)

carbon dioxide [1]

1
6(b)

Use the same mass of chips but in smaller pieces, or as a powder.

  • use smaller chips / powder with the same mass [1]
1
6(c)

There are more acid particles in the same volume of solution, so they collide with the marble more frequently each second and more successful collisions happen every second.

  • more acid particles in the same volume [1]
  • more frequent collisions with the marble [1]
2
6(d)

The acid has been used up, so it is the limiting reactant.

  • the acid is used up / it is the limiting reactant [1]
1
Total for Question 65
7(a)

Group I, the alkali metals. [1]

1
7(b)

They react with oxygen and water vapour in the air, and the oil keeps the air away from the metal.

  • they react with oxygen / water in the air [1]
1
7(c)

Reactivity increases down the Group. The outer electron is lost more easily because the atoms are larger, so the attraction between the nucleus and the outer electron is weaker.

  • reactivity increases down the Group [1]
  • the outer electron is lost more easily / weaker attraction from the nucleus [1]
2
7(d)

sodium + water → sodium hydroxide + hydrogen.

  • sodium + water → sodium hydroxide + hydrogen (all names correct) [1]
1
Total for Question 75
8(a)

cracking [1]

1
8(b)

Add bromine water and shake the mixture. The bromine water is decolourised, turning from orange to colourless.

  • add bromine water [1]
  • the bromine water is decolourised / turns from orange to colourless [1]
2
8(c)

CₙH₂ₙ [1]

1
8(d)

poly(ethene) [1]

1
Total for Question 85
9(a)

Coke, which is a source of carbon, and limestone, which is calcium carbonate.

  • coke [1]
  • limestone [1]
2
9(b)

carbon monoxide [1]

1
9(c)

It is used to make roads or as a building material.

  • road building / building material [1]
1
9(d)

Aluminium is more reactive than carbon, so carbon cannot displace it from its oxide. [1]

1
Total for Question 95

— End of mark scheme —