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 neighboring carbon atoms, creating a layered structure. One electron from each carbon atom is delocalized and can move freely between layers. This flow of delocalized electrons allows graphite to conduct electricity effectively.

The apparatus should be changed by using measuring cylinders instead of test tubes. This change is necessary because test tubes do not have the necessary graduations to accurately measure the volume of gases collected during the electrolysis.

The results in Figure 8 show that the volume of hydrogen collected increases steadily over time, indicating a constant rate of production. Initially, from 0 to about 8 minutes, the volume of chlorine collected increases at a faster rate than hydrogen. However, after 8 minutes, the rate of chlorine collection becomes constant and matches that of hydrogen, suggesting that both gases are produced at a steady rate thereafter.

One reason for the difference in volume of each gas could be due to the different molecular weights of the gases. Hydrogen is lighter than chlorine; thus, for the same number of moles, the volume of hydrogen collected would be greater than that of chlorine.

From Figure 8, the volume of chlorine collected after 20 minutes is 6.6 cm³. First, we convert cm³ to dm³:

6.6 ext{ cm}^3 = rac{6.6}{1000} ext{ dm}^3 = 0.0066 ext{ dm}^3

Next, using the molar volume at room temperature and pressure, which is 24.0 dm³ per mole, we can find the number of moles of chlorine:

ext{moles} = rac{0.0066 ext{ dm}^3}{24.0 ext{ dm}^3/ ext{mol}} = 2.75 imes 10^{-4} ext{ mol}

Thus, the amount of chlorine collected is approximately $2.75 imes 10^{-4}$ moles.