What is a PH value? The designation “pH” is an abbreviation for “power of hydrogen.” This refers to the content of acid or, to be more precise, “acid ions” (hydrogen ions H+) in the water. Pure water has very, very few acid ions (one tenth of a millionth gram per litter). This water has neither acidic nor alkaline reactions but is neutral. It has the pH value of 7.
When acid e.g. vinegar are added to water, or water absorbs the acids contained in the soil, the number of “acid ions” increase, e.g. one hundred-thousandth gram per litter. This acid water then has pH value 5.
On the other hand, there can also be even less “acid ions” present than in neutral water, e.g. one billionth gram per litter. In this case, the pH value is 9. This water is alkaline.
Equipment and Materials
Small bucket, 2 test tubes, double spoon, cooking salt, measuring beaker, distilled water, bung
plastic funnel, filter paper, pH indicator solution, pH color chart
Activity
Determine the pH value of different kinds of soil: clay soil, sand soil, marsh soil, and woodland soil.
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Method
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1. Select a certain type of soil and take samples in different places (at a depth of 5-10 cm). Place these individual samples in a small bucket and mix them well.
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2. Place approx. 2 cm of the finely crushed, crumbly soil mixture in a test tube, add the large spoon end of the double spoon full of cooking salt and 10 milliliter (measuring beaker) distilled water. Close the test tube with the bung and shake well for one to two minutes.
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3. Leave the test tube to stand until most of the soil particles have settled to the bottom.
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4. Place the plastic funnel with the folded filter paper on a second test tube. Carefully pour the soil solution through the filter without disturbing the settled particles, and collect the filtered liquid until it is aprox. 2 cm high.
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5. Now add 4 drops of pH indicator solution and carefully swirl the test tube. Compare the resulting color with color chart.
Results:
Different pH values will be obtained depending on the kind of soil involved.
For example, clay soils have a pH of 6 - 7.5, sandy soils about pH 5.5 - 6.5. Marsh soil and marsh water is fairly acid, with a pH of 2.5 - 3. Woodland soils is normally slightly acid (pH 5.5).
