The apparatus is set up as shown in the diagram below.

The thread is pulled to mix the magnesium ribbon and acid. The stopwatch is started at the same time.

The volume of hydrogen collected in the gas syringe is recorded every half-minute.

From the data collected, a graph of volume of gas produced against time taken is plotted.

From the slope of the graph, the speed of reaction can be studied.

The steeper the gradient of the graph, the faster the speed of reaction.