A student investigated the electrolysis of different substances - AQA - GCSE Chemistry - Question 6 - 2018 - Paper 1

Graphite conducts electricity due to its structure and bonding. Each carbon atom in graphite forms three covalent bonds with other carbon atoms, leaving one electron free (delocalized). These delocalized electrons can move freely through the structure, allowing graphite to conduct electricity.

The apparatus should be changed by using measuring cylinders instead of test tubes, as test tubes cannot measure volume accurately due to their lack of graduations.

The trends in Figure 8 indicate that the volume of hydrogen gas collected is directly proportional to the time, suggesting that hydrogen is produced at a constant rate. Up to 8 minutes, chlorine gas is collected at an increasing rate, but after this point, the rate of chlorine collection becomes constant at a similar rate as hydrogen.

One reason for the difference in volume of each gas could be that chlorine is produced at a different rate or that chlorine reacts with water, leading to a difference in the volume collected.

From Figure 8, assume the volume of chlorine collected after 20 minutes is 6.6 cm³. To convert this to moles, use the formula:

$\text{moles} = \frac{\text{volume (dm³)}}{24}$

First, convert 6.6 cm³ to dm³:

$6.6\, \text{cm}^3 = 0.0066\, \text{dm}^3$

Now, substituting into the formula:

$\text{moles} = \frac{0.0066}{24} = 2.75 \times 10^{-4} \text{ mol}$

Thus, the amount in moles of chlorine collected after 20 minutes is approximately $2.75 \times 10^{-4} \text{ mol}$.