The electrolysis of aqueous solutions
2 marks · EasyA student finds that the volume of chlorine gas collected during the electrolysis of concentrated sodium chloride solution is less than expected.
Explain why less chlorine gas is collected than expected.
Suggest one way you could change the experiment to collect more chlorine gas.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Some chlorine dissolves in water; it is more soluble than hydrogen. · must show chlorine dissolves in water
(b) Use a less soluble liquid (e.g. saturated sodium chloride), increase temperature, or reduce water volume/bubble the gas out rapidly.
Common mistakes: Suggesting to increase the current (irrelevant); Suggesting to increase sodium chloride concentration
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Explains that chlorine dissolves in water so not all the gas is collected.
B2 (b) · 1 mark · Suggests (1) saturating the solution with chlorine, (2) reducing the amount of water present, or (3) bubbling gas through quickly, (4) using a fume cupboard to collect gas above solution.
Worked solution
a) Less chlorine gas is collected because some of it dissolves in water and is not collected as a gas.
b) To collect more chlorine gas, you could use a saturated sodium chloride solution (to reduce chlorine solubility), reduce the volume of water, or bubble the gas out quickly to minimise dissolution.