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

The initial mass of the reaction system is recorded.

The thread is pulled to mix the calcium carbonate and acid. The stopwatch is started at the same time.

The mass of the reaction system is recorded every one-minute.

From the data collected, a graph of mass of reaction system 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.