This question is about chemical reactions and electricity - AQA - GCSE Chemistry - Question 7 - 2021 - Paper 1

The balanced half equation for the production of bromine at the positive electrode is:

$2Br^- \rightarrow Br_2 + 2e^-$

To find the total mass of copper produced, the students could filter the mixture to capture the copper, wash and dry the collected copper, and then weigh the copper and add this to the increase in the mass of the electrode.

The results show a straight line through the origin when plotting total mass of copper against time, indicating that as time doubles, the mass of copper produced also doubles, which supports direct proportionality.

When the current is increased, the mass of copper produced also increases in a linear manner. For example, at currents of 0.3 A, 0.6 A, and 0.9 A, the mass of copper produced increases, suggesting a direct proportionality.

The blue color fades because copper ions are discharged from the solution during electrolysis, leading to a decrease in the concentration of copper ions, which are responsible for the blue color.

First, calculate the number of moles of copper produced using:

$\text{Number of moles} = \frac{Q}{nF}$

where Q is the charge (in coulombs), n is the number of electrons transferred per ion (2 for copper), and F is Faraday's constant (approximately 96485 C/mol).

Total charge $Q = I \times t = 0.6 A \times 1200 s = 720 C$.

Thus,

$\text{Number of moles} = \frac{720 C}{2 \times 96485 C/mol} = 0.00378 \text{ moles}$.

Now, the number of atoms:

$\text{Number of atoms} = 0.00378 \times 6.02 \times 10^{23} \approx 2.28 \times 10^{21}$.

This value is given to 3 significant figures: 2.28 x 10^21.