A student investigated the temperature change when magnesium was added to copper sulfate solution - AQA - GCSE Chemistry Combined Science - Question 5 - 2020 - Paper 1

The copper sulfate solution was left for four minutes to allow it to reach a constant temperature, ensuring accurate measurement of temperature changes after adding magnesium.

To complete Figure 4, first draw a line of best fit through all the plotted points after 7 minutes. Then, extend this line back to the point corresponding to 4 minutes, ensuring it intersects the graph properly.

At 4 minutes, the temperature of the solution was 26.3 °C. After 7 minutes, it stabilized at 17.5 °C. Therefore, the temperature change for the reaction is calculated as:

$ext{Temperature change} = 26.3 - 17.5 = 8.8 ext{ °C}$

The temperature of the mixture decreases after 7 minutes because the reaction between magnesium and copper sulfate solution generates heat initially, but as the reaction proceeds, heat is lost to the surroundings, cooling the solution down, or the solution takes time to return to room temperature.

Metal Q is likely to be aluminum or zinc. This is because these metals are less reactive than magnesium, which would explain the smaller temperature change observed in the experiment.

To find the mass of copper sulfate in 30.0 cm³, convert the volume to dm³:

$30.0 ext{ cm}³ = 0.030 ext{ dm}³$

Then calculate moles using the concentration:

$ext{Moles} = 0.100 ext{ moles/dm}³ imes 0.030 ext{ dm}³ = 0.00300 ext{ moles}$

Finally, calculate the mass using the relative formula mass (Mr):

$ext{Mass} = ext{Moles} imes ext{Mr} = 0.00300 imes 159.5 = 0.4785 ext{ g}$

Thus, the mass of copper sulfate in 30.0 cm³ of the solution is approximately 0.48 g.