Page 183 - Science Coursebook

Reference

Anomalous results
Sarah did an experiment to find out how temperature affects the rate of reaction

between magnesium and hydrochloric acid. She used acid at different temperatures
and measured the volume of gas produced.
Sarah made three measurements for temperature. This table shows her results.

Temperature of Volume of gas produced in one minute / cm 3
acid / °C 1st try 2nd try 3rd try Mean

10 4.5 4.2 4.6
20 9.1 9.3 8.9
30 18.0 17.9 18.1
40 31.1 36.0 36.2

Sarah thought that one of her results didn’t look right. Can you spot which
one it is?
A result like this, that does not fit the pattern of all the other results, is called an

anomalous result.

If you get something that looks like an anomalous result, there are two things that you
can do.

1 The best thing to do is to try to measure it again.
2 If you can’t do that, then you should ignore the result. So Sarah should not use this
result when she is calculating the mean. She should use only the other two results
for that temperature, add them up and divide them by two.

Questions

1 Which is the anomalous result in Sarah's table?
2 Explain how you picked out the anomalous result.
3 Calculate the mean volume of gas produced in one minute for each
temperature of acid. Remember – don’t include the anomalous result in
your calculation!

Spotting an anomalous result in a results table can be quite difficult. It is often much
easier if you have drawn a graph.
Rajesh did an experiment to investigate how adding ice to water changed its
temperature. He added a cube of ice to 500 cm of water and stirred the water until
3
the ice had completely melted. Then he measured the temperature of the water
before adding another ice cube. The graph on the next page shows
his results.

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