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 that the measurement of temperature change due to adding magnesium is accurate.

To complete Figure 4, draw a line of best fit that connects all data points from 7 minutes onward. Then, extend this line backward to intersect the temperature line at the 4-minute mark.

The temperature of the solution at 4 minutes, as seen in Figure 4, is approximately 26.3 °C. Assuming the final temperature after adding magnesium is 17.5 °C, the temperature change can be calculated as:

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

Thus, the temperature change for the reaction is 8.8 °C.

The temperature of the mixture decreases after 7 minutes because the reaction between magnesium and copper sulfate solution tends to reach completion, resulting in the system losing energy to the surroundings. This causes the solution to cool down to reach room temperature.

Metal Q could be aluminum or zinc. The reason is that these metals are less reactive than magnesium, which corresponds to the smaller temperature change observed in the experiment.

First, determine the concentration of the copper sulfate solution:

Given: 0.100 moles in 0.500 dm³.

To calculate the concentration:

ext{Concentration} = rac{0.100 ext{ moles}}{0.500 ext{ dm}^3} = 0.200 ext{ mol/dm}^3

Now, calculate the amount of moles in 30.0 cm³ (or 0.030 dm³):

$ext{Moles} = 0.200 ext{ mol/dm}^3 imes 0.030 ext{ dm}^3 = 0.006 ext{ moles}$

Now, calculate the mass using the molar mass of CuSO₄:

$ext{Mass} = ext{Moles} imes ext{Molar mass} = 0.006 ext{ moles} imes 159.5 ext{ g/mol} = 0.957 ext{ g}$

Thus, the mass of copper sulfate in 30.0 cm³ of this solution is 0.957 grams.