This question is about electrolysis - AQA - GCSE Chemistry: Combined Science - Question 5 - 2019 - Paper 1

1. Aluminium oxide
2. Cryolite

Cu²⁺ + 2e^- → Cu

2 Cl^- → Cl₂ + 2e^-

1. The concentration or volume of the copper chloride solution may have been different from expected.
2. There might have been errors in timing during the electrolysis process.

Using Figure 5, we can see that the mass of copper produced is a linear function of time. If the expected mass produced each minute is around 5.4 mg, then over 24 hours (1440 minutes), the expected mass would be:

$ext{Expected mass} = 5.4 ext{ mg} imes 1440 ext{ minutes} = 2592 ext{ mg}$

From Figure 6, the mass of the negative electrode at the start of the experiment is determined to be 5 grams.

To calculate the gradient of the line in Figure 6, we can use the formula:

ext{Gradient} = rac{Y}{X} Where Y is the change in mass (in grams) over the change in time (in hours). Given that the mass increased from 5 grams to 10 grams over 10 hours:

ext{Gradient} = rac{10 - 5}{10 - 0} = 0.5 ext{ grams per hour}