The student is asked to explain why data was collected until two successive readings agreed, plot a graph of volume of hydrogen against time, and determine the time at which the reaction went to compl

Data was collected until two successive readings agreed to ensure that the reaction had gone to completion. This indicates that all the limiting reactant (magnesium) had been consumed, and no more hydrogen gas was being produced, thus giving the maximum possible volume of gas.

To plot the graph:

• Draw a set of axes. Label the x-axis "Time (minutes)" and the y-axis "Volume of H₂ (cm³)".
• Choose appropriate scales for both axes to accommodate the data range (Time: 0-150 minutes, Volume: 0-101 cm³).
• Plot the given data points: (0,0), (5,30), (10,50), (15,65), (20,75), (30,89), (40,94), (60,100), (100,101), (150,101).
• Draw a smooth curve through the plotted points. The curve should be steepest at the beginning and gradually flatten out as the reaction proceeds.

From the graph

The reaction went to completion when the volume of hydrogen gas stopped increasing. From the data, the volume reaches 101 cm³ at 100 minutes and remains 101 cm³ at 150 minutes. Therefore, the reaction completed at:

To determine the volume at 50 minutes, you would read the value from the graph at $x = 50$ minutes.
Based on linear interpolation between 40 minutes (94 cm³) and 60 minutes (100 cm³):
Volume at 50 min = $94 + \frac{50-40}{60-40} \times (100-94)$
Volume at 50 min = $94 + \frac{10}{20} \times 6$
Volume at 50 min = $94 + 3 = 97 \text{ cm}^3$
The volume of hydrogen gas collected after 50 minutes is approximately:

If there were a little heating:

• The initial rate of reaction would increase, so the curve would be steeper at the beginning.
• The reaction would reach completion faster, meaning the curve would flatten out at an earlier time.
• The final volume of hydrogen gas collected would remain the same (101 cm³) because the amount of limiting reactant (magnesium) is unchanged.