O-LevelChemistryStoichiometry5070/21 · Oct/Nov 2019 · Q213 Marks

Sodium is a metal.

(a)State two physical properties of sodium which are different from most other metals.[2]
(b)Complete the electronic configuration of a sodium atom. Show all electrons. [Figure: Electron shell diagram for Na with inner shells filled but outer shell incomplete][1]
(c)The equation shows the reaction of sodium with water. 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) Calculate the minimum mass of sodium, in grams, needed to produce 300 cm³ of hydrogen gas at room temperature and pressure. Give your answer to three significant figures. mass of sodium ................................................................ g [3][3]
(d)Sodium reacts with oxygen to form the ionic solid sodium oxide, Na2O. Explain, in terms of movement of electrons, how Na2O is formed by the reaction of sodium with oxygen.[3]
(e)(i)Suggest one other physical property of sodium chloride.[1]
(e)(ii)State the products formed at the anode and cathode when concentrated aqueous sodium chloride is electrolysed. product at anode ........................................................................................................................ product at cathode .................................................................................................................... [1][1]
(e)(iii)Describe a test for chloride ions. test ..................................................................................................................................................... observation .................................................................................................................................... [2][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.

2(a) Any two from:
low melting point / low boiling point (1)
low density (1)
soft (1)
2(b) drawing of electronic structure of 2.8.1
2(c) mol H2 = 300/24000 OR 0.0125 (1)
moles sodium 2 × 0.0125 OR 0.025 (1)
mass of sodium = 0.575 g (1)
2(d) sodium (atom) loses electron(s) (1)
oxygen (atom or molecule) gains electron(s) (1)
two electrons gained by oxygen (atom) (1)
2(e)(i) high melting point/ high boiling point / does not conduct electricity when solid / does conduct electricity when molten / does conduct electricity when in aqueous solution
2(e)(ii) anode: chlorine AND cathode: hydrogen
2(e)(iii) (add nitric acid) then (aqueous) silver nitrate (1)
white precipitate (1)