Question 18M.2.sl.TZ1.2
| Date | May 2018 | Marks available | [Maximum mark: 8] | Reference code | 18M.2.sl.TZ1.2 |
| Level | sl | Paper | 2 | Time zone | TZ1 |
| Command term | Describe, Estimate, Outline, State, Suggest | Question number | 2 | Adapted from | N/A |
Calcium carbide, CaC2, is an ionic solid.
Describe the nature of ionic bonding.
[1]
electrostatic attraction AND oppositely charged ions
[1 mark]
State the electron configuration of the Ca2+ ion.
[1]
1s22s22p63s23p6
OR
[Ar]
[1 mark]
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]
«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]
Suggest two reasons why solid calcium has a greater density than solid potassium.
[2]
Any two of:
stronger metallic bonding
smaller ionic/atomic radius
two electrons per atom are delocalized
OR
greater ionic charge
greater atomic mass
Do not accept just “heavier” or “more massive” without reference to atomic mass.
[2 marks]
Outline why solid calcium is a good conductor of electricity.
[1]
delocalized/mobile electrons «free to move»
[1 mark]
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]
pH > 7
Accept any specific pH value or range of values above 7 and below 14.
[1 mark]