Drawing and displaying graphs is challenging for many students. You can find more information about drawing graphs here, in the Maths skills course.

To display the data from the experiments where we have looked at the transmission of light through a sample of iodine we can either use arbitrary units or, if the colorimeter has been calibrated, we can plot a graph of concentration of iodine vs time.

Here is an example of a graph obtained from the experiment.

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Looking at the graph we could write a commentary to describe the progress of the reaction. Students often have difficulty with this so it's worth giving them the opportunity to describe graphs such as the one above. Here are some key questions.

What does 100% transmission indicate about the progress of the reaction?

This indicates that the reaction is complete. In this experiment the reaction is complete at 40 seconds.

At what time in the experiment does the reaction seem to be at its fastest?

The reaction is at its fastest in the first 5 seconds. This is shown on the graph by the presence of a steep straight line.

What is the advantage of displaying data in a graph such as the one drawn above?

It allows us to see the progress of the reaction over time. The gradient of the line indicates the rate so we can make comparisons.

How can we compare the actual rate at different times throughout the experiment?

This can be achieved by drawing a tangent to the curve.