O-LevelChemistryAcids, Bases & Salts5070/22 · May/June 2020 · Q710 Marks

This question is about some of the oxides of the elements in Period 3.

(a)State the electronic configuration of the negative ion in sodium oxide, Na2O.[1]
(b)Magnesium oxide is an insoluble base that can be used to prepare pure magnesium sulfate crystals. Describe the essential practical details for the preparation of pure magnesium sulfate crystals from magnesium oxide.[4]
(c)(i)An oxide of phosphorus contains 43.7% by mass of phosphorus. Show that the empirical formula for this oxide is P2O5.[2]
(c)(ii)A sample of this oxide has a mass of 2.56 g. The sample contains 0.00901 mol of the oxide. Calculate the relative molecular mass and hence the molecular formula for this oxide of phosphorus. relative molecular mass .............................................................. molecular formula ..................................................................... [2][2]
(d)State the structure and bonding in silicon dioxide, SiO2.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[1] 7(a) 2.8
[1] 7(b) use sulfuric acid (1)
[1] 7(b) excess base (added to warm acid) (1)
[1] 7(b) mixture filtered (and the filtrate collected) (1)
[1] 7(b) filtrate partially evaporated and then left to crystallise / filtrate left to crystallise / filtrate heated until saturated and then left to form crystals (1)
[1] 7(c)(i) mole ratio P to O is 43.7/31 to 56.3/16 OR 1.41 to 3.52 (1)
[1] 7(c)(i) divide by smallest 1.41/1.41 to 3.52/1.41 = 1 to 2.5 and evidence of multiplying by 2 (1)
[1] 7(c)(ii) 284 (1)
[1] 7(c)(ii) P4O10 (1)
[1] 7(d) giant covalent (1)

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