A-LevelChemistryNitrogen and sulfur9701/22 · Oct/Nov 2024 · Q319 Marks

Nitrogen and phosphorus are elements in Group 15 of the Periodic Table.

(a)Nitrogen is found in inorganic compounds such as nitrogen oxides (NOx), nitrates and nitric acid.
(a)(i)Identify one natural and one man-made occurrence of nitrogen oxides in the atmosphere. natural man-made[2]
(a)(ii)Write an equation to describe the role of NO₂ in the direct formation of acid rain.[1]
(a)(iii)Peroxyacetyl nitrate, PAN, is a component of photochemical smog. Describe how PAN forms from NO₂.[1]
(a)(iv)Nitric acid reacts with basic oxides to form nitrates. Write an equation for the reaction of nitric acid with calcium oxide.[1]
(a)(v)Describe what is seen when solid calcium nitrate is heated strongly.[1]
(b)A common test for nitrates is the reaction with NaOH and Al. Equation 1 shows the reaction. equation 1 3NO₃⁻ + 8Al + 5OH⁻ + 18H₂O → 3NH₃ + 8[Al(OH)₄]⁻
(b)(i)Deduce the oxidation state of nitrogen in NO₃⁻.[1]
(b)(ii)Identify the species that is oxidised in equation 1.[1]
(b)(iii)NH₃ is a basic gas. Describe how NH₃ is able to act as a base.[1]
(b)(iv)Suggest the shape of the [Al(OH)₄]⁻ ion.[1]
(c)Fig. 3.1 shows a sketch of some of the ionisation energies of phosphorus, P. [Figure 3.1]
(c)(i)Construct an equation to represent the third ionisation energy of P.[1]
(c)(ii)Complete the graph in Fig. 3.1 to show the third to sixth ionisation energies of P.[2]
(d)Complete Table 3.1 to show the properties of nitrogen and phosphorus in their standard states. Table 3.1 | | nitrogen | phosphorus | |---|---|---| | state and appearance of standard state | colourless gas | white solid | | electrical conductivity | | poor | | type of bonding | | | | type of structure | simple | |[2]
(e)A form of solid nitrogen has a lattice structure similar to solid iodine. Identify the type of lattice structure of solid nitrogen.[1]
(f)At very high temperatures, phosphorus can form P₂ molecules. P₂ contains a triple bond, P≡P.
(f)(i)Describe the formation of the P≡P bond in terms of orbital overlap.[2]
(f)(ii)The bond energy of P≡P is 485 kJ mol⁻¹. The bond energy of N≡N is 944 kJ mol⁻¹. Compare the reactivity of P₂ and N₂. Explain your answer.[1]

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 2024). The mark or mark type is shown in brackets.

[1] (natural = )lightning
[1] (man-made = )internal combustion engines
[1] 2NO₂ + H₂O → HNO₂ + HNO₃ OR 4NO₂ + O₂ + 2H₂O → 4HNO₃
[1] It / NO₂ reacts with (unburned) hydrocarbons / VOCs ALLOW reaction of unburned hydrocarbons / VOCs in presence of NO₂
[1] 2HNO₃ + CaO → Ca(NO₃)₂ + H₂O
[1] brown fumes given off
[1] (+)5 / V
[1] aluminium / Al
[1] (NH₃ is an) H⁺ acceptor
[1] tetrahedral
[1] P²⁺(g) → P³⁺(g) + e⁻
[1] general increase
[1] increase in IE between IE5 and IE6 is noticeably the largest increase between IEs shown
[2] element | nitrogen | phosphorus ---|---|--- state and appearance | colourless gas | white solid electrical conductivity | • poor | poor type of bonding | • covalent | • covalent type of structure | simple | • simple
[1] simple molecular (lattice structure)
[1] M1 one sigma / σ bond AND head-on (overlap of) p / sp (orbitals)
[1] M2 two pi / π bond(s) AND side-on (overlap of /involving) p (orbitals)
[1] P≡P is much weaker so P₂ is more reactive (than N₂)