The word equation for the reaction between magnesium and dilute hydrochloric acid is magnesium + hydrochloric acid → magnesium chloride + hydrogen The reaction was carried out using the apparatus shown in Figure 6 - Edexcel - GCSE Chemistry Combined Science - Question 4 - 2019 - Paper 1

The mass of the flask decreases because hydrogen gas is released into the atmosphere during the reaction. As the magnesium ribbon reacts with the hydrochloric acid, it produces magnesium chloride and hydrogen gas. Since the gas escapes the closed system, the total mass of the flask and its contents is reduced.

To find the volume of hydrogen gas produced, we can refer to the data shown in Figure 7. At 5 minutes, the loss in mass of the flask is approximately 0.008 g. Given that 1 mole of hydrogen gas (H₂) has a molar mass of about 2 g, we can calculate the volume of gas produced using the ideal gas laws and standard conditions, where 1 mole of gas occupies 24,000 cm³. Therefore, the volume of hydrogen produced can be determined by:

$Volume = \frac{mass\ of\ H_2}{molar\ mass\ of\ H_2} \times 24000$

Substituting the values:

$Volume = \frac{0.008 \text{ g}}{2\text{ g/mol}} \times 24000 = 96 \text{ cm}^3$

The graph should depict the loss in mass (in grams) on the y-axis against time (in minutes) on the x-axis. The curve should start at the origin and rise sharply at first, indicating a rapid reaction, and then level off as the reaction nears completion, resembling the graph shown in Figure 7. The gradient should decrease progressively.