Electrolysis turns up in 0620 Paper 6 as apparatus and method questions, and a weighed-cathode experiment is exactly the kind of Question 1 Paper 5 can set. By hand, clean copper electrode C on emery paper, rinse it in distilled water and then propanone, dry it and read the balance. Pour the copper(II) sulfate into the cell, clip the electrodes to the right leads, switch on, slide the variable resistor until the ammeter shows the current you want and time 20 minutes on the stopwatch. Rinse, dry and reweigh, at five currents. Then plot your own graph with a ruled line through the origin, spot the anomalous result and evaluate the method. Every attempt gives different readings. Allow about 40 minutes.
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Headings with units, every current as the ammeter showed it and every mass as the balance showed it (both to 2 decimal places), the mass of copper deposited by subtraction, five 20-minute experiments with electrode C always the cathode and currents spread from about 0.2 A to 1.0 A, and an accuracy mark for masses close to the true values.
A sensible scale for the mass axis, every point plotted within half a small square, and a ruled best-fit straight line that ignores the anomalous point and passes through the origin.
The anomalous experiment and a reason that matches which side of the line it lies, a mass read from your own line, and the conclusion that the mass deposited is directly proportional to the current.
Pink-brown copper on the cathode and a thinner anode, why the cathode is rinsed with water and then propanone, a source of error, an improvement with its reason, and a safety precaution.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.