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Introduction
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The pH scale measures the acidity or the alkalinity of a substance. The pH scale goes from pH1 to pH14. pH1 is the most acid, pH14 is the most alkaline and pH 7 is neutral (neither acid nor alkaline).

Living things cannot tolerate a pH much above or below pH7 (neutral).

Aim
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To find the pH of the different soil samples taken from the deciduous forest.

Method
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1. Set up the apparatus as shown in the diagram below.

2. Shake the test tube vigorously for a few seconds. (NB. Place your thumb over the rubber bung to stop it falling out. Shake until the soil sample completely mixes with the rest of the contents of the test tube.)

3. Label your test tube and replace it in the test tube rack. Leave it until the contents have settled.

4. Repeat points 1., 2. and 3. with the three other soil samples.

5. Compare the colours of the liquid in each of the four test tubes with the standards provided. Record your results.

Results
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You will be provided with the pH standards for the indicator liquid you are using.

N.B. The barium sulphate (US spelling = sulfate) powder is neutral. It is included in each tube to bind with the particles of soil so that they fall to the bottom of the tube after it has been shaken. This allows you to see the colour of the liquid more easily.

Conclusion

Write a conclusion to this experiment. 
Are there any differences in the pH levels of the four soil layers?
Explain the reason for any differences.
If your results are not as you might have expected, suggest why.

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©  Shirley Burchill 2008