Scientific data is collected, presented and then analysed. It is important to evaluate the quality of data before drawing a conclusion.

A graph helps to analyse data and can be used to draw a conclusion.

When plotting a graph:

- choose axis scales so that the plotted points occupy at least half the space available (this will help make the graph easier to read)
- label both axes, including the units
- think about whether the line should pass through the origin (0,0)
- choose intervals along the scale that make it easy to plot the points and read off values, eg increments of 2, 5 or 10
- a point that is not near the best fit line is anomalous - it needs to be explained before it can be ignored
- after plotting the point, draw a line of best fit - remember this can be curved

A lot can be learnt by looking at the shape of a graph. The gradient is the slope of the graph. For example, when looking at a graph of mass produced against time, the gradient of the graph shows the mass produced per second. This is the rate of reaction.

- Question
How does the rate of reaction change over time?

- Imagine walking along the graph. Describe how the gradient changes:
- it starts very steep and then gets gradually less steep until it is horizontal

- Turn this into a description of the rate of reaction:
- the rate of reaction is very fast at the start but gradually slows down until the reaction stops

- Imagine walking along the graph. Describe how the gradient changes:

Finding values within the range originally measured is called interpolation.

To interpolate a graph, read up from the horizontal axes, then across to find the new value.

Finding values beyond the range that was originally measured is called extrapolation.

To extrapolate a graph, first extend the line. Then read up from the horizontal axis and across to find the new value.