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Date	May 2018	Marks available	1	Reference code	18M.2.sl.TZ1.2
Level	SL	Paper	2	Time zone	TZ1
Command term	Describe	Question number	2	Adapted from	N/A

Question

Calcium carbide, CaC₂, is an ionic solid.

Describe the nature of ionic bonding.

[1]

State the electron configuration of the Ca²⁺ ion.

[1]

When calcium compounds are introduced into a gas flame a red colour is seen; sodium compounds give a yellow flame. Outline the source of the colours and why they are different.

[2]

Suggest two reasons why solid calcium has a greater density than solid potassium.

[2]

d.i.

Outline why solid calcium is a good conductor of electricity.

[1]

d.ii.

Calcium carbide reacts with water to form ethyne and calcium hydroxide.

CaC₂(s) + H₂O(l) → C₂H₂(g) + Ca(OH)₂(aq)

Estimate the pH of the resultant solution.

[1]

Markscheme

electrostatic attraction AND oppositely charged ions

[1 mark]

1s²2s²2p⁶3s²3p⁶

[Ar]

[1 mark]

«promoted» electrons fall back to lower energy level

energy difference between levels is different

Accept “Na and Ca have different nuclear charge” for M2.

[2 marks]

Any two of:

stronger metallic bonding

smaller ionic/atomic radius

two electrons per atom are delocalized

greater ionic charge

greater atomic mass

Do not accept just “heavier” or “more massive” without reference to atomic mass.

[2 marks]

d.i.

delocalized/mobile electrons «free to move»

[1 mark]

d.ii.

pH > 7

Accept any specific pH value or range of values above 7 and below 14.

[1 mark]

Examiners report

[N/A]

d.i.

[N/A]

d.ii.

[N/A]

Syllabus sections

Core » Topic 4: Chemical bonding and structure » 4.1 Ionic bonding and structure

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State the type of bonding in potassium chloride which melts at 1043 K.
22M.1.sl.TZ2.9:
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17M.1.sl.TZ2.10:
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Between hydrogen and oxygen in hydrogencarbonate:
21M.1.sl.TZ2.11:
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