A-LevelChemistryChemical periodicity9701/23 · Oct/Nov 2019 · Q213 Marks

(a) Complete the table to give details of the type of bonding and structure shown by some of the oxides of Period 3 elements. | | Na₂O | MgO | Al₂O₃ | SiO₂ | SO₃ | |---|---|---|---|---|---| | boiling point/°C | 1275 | 3670 | 2977 | 2950 | 45 | | nature of oxide | basic | basic | amphoteric | acidic | acidic | | bonding | | | | | | | structure | | | | | |

(a)Complete the table to give details of the type of bonding and structure shown by some of the oxides of Period 3 elements. | | Na₂O | MgO | Al₂O₃ | SiO₂ | SO₃ | |---|---|---|---|---|---| | boiling point/°C | 1275 | 3670 | 2977 | 2950 | 45 | | nature of oxide | basic | basic | amphoteric | acidic | acidic | | bonding | | | | | | | structure | | | | | |[2]
(b)(i)Explain why the boiling point of SiO₂ is much higher than the boiling point of SO₃.[3]
(b)(ii)Al₂O₃ is an amphoteric oxide. Explain what is meant by the term amphoteric. Use chemical equations to illustrate your answer.[3]
(b)(iii)State what you would observe when a small sample of Na₂O is placed in water.[1]
(c)(i)Selenium is a Group 16 element which shows similar chemical reactions to sulfur. Selenium reacts with fluorine to form SeF₆ molecules. Predict the shape of a molecule of SeF₆.[1]
(c)(ii)The most stable oxide of selenium is SeO₂. Gaseous SeO₂ reacts to form a solid polymer, as shown. In the reaction one Se=O is replaced by two Se–O to form a polymer. [Figure showing Se=O dimerizing to form a polymer] The bond enthalpy of Se=O is 514 kJ mol⁻¹. Use these data to calculate the bond enthalpy, in kJ mol⁻¹, of Se–O.[2]
(c)(iii)SeO₂ shows similar chemical reactions to SO₂. Suggest an equation to show the reaction of SeO₂ with aqueous sodium hydroxide, NaOH.[1]

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Mark scheme

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

[2] (a) Bonding: ionic, ionic, ionic, covalent, covalent. Structure: giant, giant, giant, giant / macromolecular, simple / molecular. Award one mark for each correct row.
[3] M1: SiO₂ has a network of strong bonds / SiO₂ has many strong bonds M2: SO₃ has weak intermolecular forces OR weak VdW forces (between molecules) M3: high(er) / more energy required to break bonds than overcome forces (between molecules)
[3] M1: reacts with both acid and base / alkali M2: use any equation with Al₂O₃ and an acid, e.g. Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O M3: use any equation with Al₂O₃ and a base / alkali, e.g. Al₂O₃ + 2NaOH + 3H₂O → 2NaAl(OH)₄
[1] solid dissolves / disappears OR gets warm / hot
[1] octahedral
[2] M1: use of the correct expression in terms of specific bond energies. (514 - xEse-o = -346) M2: use of correct stoichiometry AND correct processing of expression given in M1. Provided the values 514 and 346 are used. (514 - 2Ese-o = −346) = (+)430 (kJ mol⁻¹)
[1] SeO₂ + 2NaOH → Na₂SeO₃ + H₂O

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