Fig. 15.1 shows a piece of laboratory apparatus used in electrolysis experiments. It has two terminals, one marked positive and one marked negative, and a d...
Question 1 Report
Fig. 15.1 shows a piece of laboratory apparatus used in electrolysis experiments. It has two terminals, one marked positive and one marked negative, and a dial to set the voltage.
(a) Name the piece of apparatus shown in Fig. 15.1. [1]
(b) State the use of this apparatus in an electrolysis experiment. [1]
(c) Explain why a direct current supply is used for electrolysis rather than an alternating current supply. [1]
(d) State why carbon (graphite) rods are often used as the electrodes. [1]
Answer Details
Labelled answer diagram:
Fig. 15.1 shows the power supply used to drive an electrolysis. This question tests apparatus recognition and why the choices of current and electrode matter.
(a) The apparatus is a d.c. power supply (power pack, or a battery) [1]. The positive and negative terminals and the voltage dial are the clues.
(b) Its use is to provide the direct current that drives the electrolysis, i.e. it pushes current through the electrolyte so the ions are discharged at the electrodes [1].
(c) A direct current is used rather than alternating current because with d.c. each electrode stays permanently as the cathode or the anode, so each product forms at a fixed, known electrode [1]. With a.c. the terminals would keep swapping, so the products would form and re-dissolve at each electrode and could not be collected separately.
(d) Carbon (graphite) rods are used because carbon is inert (unreactive) and it conducts electricity, so it carries the current without reacting or contaminating the products during electrolysis [1].
Exam tip: "inert" plus "conducts" is the two-part reason carbon electrodes are chosen; naming only one usually loses the mark.
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