A-LevelChemistryChemical periodicity9701/22 · Oct/Nov 2019 · Q119 Marks

In the Periodic Table, the p block contains elements whose outer electrons are found in the p subshell.

(a)(i)Draw the shape of a p orbital.[1]
(a)(ii)Write an equation to show the first ionisation energy of silicon.[1]
(a)(iii)Explain why there is a general increase in first ionisation energies of the elements across Period 3.[2]
(a)(iv)Element A is in the p block. The graph shows the successive ionisation energies for the removal of the first ten electrons of A. [Figure: Graph showing ionisation energy vs. number of electrons removed] State and explain the group of the Periodic Table that element A belongs to.[2]
(b)(i)Silicon is found in many compounds in the Earth's crust. Silicon has only three naturally occurring isotopes, 28Si, 29Si and 30Si. The table shows data for 28Si, 29Si and 30Si. | | 28Si | 29Si | 30Si | |---|---|---|---| | relative isotopic mass | 28.0 | 29.0 | 30.0 | A sample of silicon contains 92.2% 28Si. The total percentage abundance of 29Si and 30Si in the sample is 7.8%. The relative atomic mass, Ar, of silicon in the sample is 28.09. Calculate the percentage abundance of 30Si. Give your answer to one decimal place.[3]
(b)(ii)Silicon reacts with nitrogen gas to form Si3N4. Si3N4 is a solid with a melting point of 1900 °C. It is insoluble in water and does not conduct electricity when molten. Suggest the type of bonding in and structure of Si3N4. Explain your answer.[3]
(c)(i)Sulfur-containing compounds, such as C2H5SH, are found in fossil fuels, and produce SO2 when they are burned. Write the equation to show the complete combustion of C2H5SH.[1]
(c)(ii)State why the presence of SO2 in the atmosphere has environmental consequences. Describe one of the consequences on the environment.[2]
(d)(i)SO2 can react with ozone, O3, to form SO3 in two different reactions. In one reaction, SO2 reacts with O3 until a dynamic equilibrium is established. SO2(g) + O3(g) ⇌ SO3(g) + O2(g) State and explain the effect of an increase in pressure on the composition of the equilibrium mixture.[2]
(d)(ii)In the other reaction, a different equilibrium is established at 300 K as shown. 3SO2(g) + O3(g) ⇌ 3SO3(g) ΔH = +462.3 kJ mol-1 Suggest a temperature needed to increase the yield of SO3 at equilibrium. Explain your answer.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[1] 8
[1] Si(g) → Si+(g) + e-
[2] M1: similar shielding AND increase in proton number / atomic number / nuclear charge
[2] M2: increased nuclear attraction
[2] M1: 3 OR 13
[2] M2: large(r) increase between third and fourth ionisation energies OR large(r) increase after third electron removed
[3] M1: (92.2 × 28) + (29Si x 29) + (30Si x 30) / 100 = 28.09
[3] M2: (x =) 6.6 OR 28.09 = 28.078 + x (where x = abundance of Si-29)
[3] M3: 7.8 – M2 calculated correctly to one decimal place (or more) (=) 1.2%
[3] M1 giant (molecule)
[3] M2 strong covalent bonds (between atoms / particles)
[3] M3 no mobile charged particles / carriers
[1] C2H5SH + 4½O2 → 2CO2 + 3H2O + SO2
[2] M1: (causes) acid rain OR reacts/dissolves with (rain)water (vapour) to form (sulfuric / sulfurous) acid
[2] M2: one point from the following list. lowers pH / increases acidity of rivers / lakes / oceans / water supplies / seas / soil / ground water OR kills/harms / damages fish OR kills / harms / damages plants / damages coral / aquatic life / plants / crops / trees or deforestation OR leaches (toxic) aluminium (ions / salts) from soil (into rivers / lakes) OR leaches away soil nutrients / soil unfit for agriculture OR damages / weathers / erodes / destroys buildings / statues
[2] M1: no effect / none
[2] M2: equal mol(es) (of gas) on both sides (of equilibrium / equation) owtte
[2] M1: (forward reaction is) endothermic
[2] M2: Any temperature higher than 300 K