A-LevelChemistryChemical periodicity9701/22 · Oct/Nov 2024 · Q215 Marks

Oxygen is a Group 16 element.

(a)(i)Write equations for the following reactions. • sodium and oxygen • sulfur and oxygen[2]
(a)(ii)Draw a dot-and-cross diagram to show the species present in Al₂O₃. Draw outer electrons only.[1]
(a)(iii)The maximum oxidation state of the Period 3 elements in their oxides varies across the period. State and explain the variation.[2]
(b)H₂O reacts with both inorganic and organic compounds.
(b)(i)Complete Table 2.1 to give details of the reactions of some Period 3 oxides with H₂O. Table 2.1 | Period 3 oxide | product of reaction with H₂O | pH of solution formed | |---|---|---| | MgO | Mg(OH)₂ | | | P₄O₁₀ | | |[2]
(b)(ii)Write an equation for the reaction of CH₃CN with H₂O in acidic conditions. CH₃CN + ......H₂O + ......H⁺ → [1]
(b)(iii)Draw the structures of the two alcohols formed in the reaction shown in equation 1. H₃PO₄ equation 1 C₃H₆(g) + H₂O(g) ⟶ C₃H₈O(g)[2]
(b)(iv)Explain why alcohols are less acidic than water.[2]
(c)Fig. 2.1 shows the boiling points of H₂O and other Group 16 hydrides. [Figure 2.1]
(c)(i)Explain the trend in the boiling points of the Group 16 hydrides H₂S to H₂Te.[2]
(c)(ii)Explain why the boiling point of H₂O is much higher than that of H₂S.[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] M1 4Na + O₂ → 2Na₂O
[1] M2 S + O₂ → SO₂
[1] Al³⁺ [O²⁻] (dot-and-cross diagram showing Al³⁺ and O²⁻ ions with correct outer electrons)
[1] it increases
[1] as number of valence electrons (which can be used in bonding / lost / shared / donated) increases
[2] Period 3 oxide | product of rxn with water | pH of solution formed ---|---|--- MgO | Mg(OH)₂ | • 8 ≤ pH < 12 P₄O₁₀ | • H₃PO₄ | • 1 ≤ pH ≤ 4
[1] CH₃CN + 2H₂O + (1)H⁺ → CH₃COOH + NH₄⁺
[2] (Structure of propan-1-ol and propan-2-ol) CH₃CH₂CH₂OH and CH₃CH(OH)CH₃
[1] alkyl groups are electron donating / have positive inductive effect.
[1] strengthens the O—H bond / makes H⁺ less likely to be donated
[1] (molecules) H₂S to H₂Te / they have greater number of electrons
[1] stronger instantaneous dipole-induced dipole / London dispersion forces OR more energy required to overcome the instantaneous dipole-induced dipole / London dispersion forces
[1] (only) H₂O has hydrogen bonding AND hydrogen bonding (much) stronger than the other intermolecular forces OR H₂O has hydrogen bonding AND because of higher electronegativity of O compared to S OR stronger van der waals' forces because (only) H₂O has hydrogen bonding OR hydrogen bond AND increased strength of permanent dipoles in H₂O outweighs the increase in strength of id-id in the others

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.