Youth water quality tests – Part 4 – pH
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EmailTeach students about science by playing in the river! You can learn about the pollution in the river by studying the pH.
Continuing a series by Michigan State University Extension, this is the fourth article about testing water quality with students. By conducting some simple tests, students can learn about how clean or polluted nearby streams are. By doing further investigation, the students can identify the problem and help to improve the river. In 1984, a group of concerned students at a high school located along the polluted Huron River in Ann Arbor, Mich. created the international program called Global Rivers Environmental Education Network (GREEN). Their teacher contacted Dr. William Stapp at the University of Michigan, and together they developed the comprehensive educational program.
Young people can partner with local schools, watershed groups, lake associations, drain commissioner offices, conservation districts, nature centers or other groups to conduct these tests.
The background
Scientists use this measurement to determine if a liquid is either an acid, neutral or basic (alkaline). Most living things do well around seven on the pH scale. Since the scale goes from one to 14, the further the water is in either direction from seven, the greater stress there is on living things. Normal fresh water lakes and streams will show a pH around the six to eight range.
Pure water is neutral at a pH of seven. Anything higher than seven is basic, while anything lower than seven is acidic.
Strong acids, like “battery acid,” would have pH around one, while a strong base like “Drano” would have a pH near 14. Low pH (acidic) could be caused from acid rain or industrial pollution. High pH values (basic) could be caused by industrial dumping or natural minerals leaching into the water, ashes from burned materials, soaps and detergents.
Since pH is on a logarithmic scale, something with a pH of six is ten times as acidic as a liquid with a pH of seven. A liquid with a pH of five is 100 times as acidic as a liquid with a pH of seven.
|
pH |
Example |
|
1 |
Concentrated sulfuric acid |
|
2 |
Vinegar or lemon juice |
|
3 |
Orange juice or soda pop |
|
4 |
Tomato juice |
|
5 |
Coffee |
|
6 |
Urine |
|
7 |
Pure water |
|
8 |
Sea Water |
|
9 |
Baking Soda |
|
10 |
Milk of Magnesia |
|
11 |
Ammonia |
|
12 |
Soapy Water |
|
13 |
Bleach |
|
14 |
Drain Cleaner |
The test
There are many testing kits available for pH. They can be purchased at pool supply companies, pet stores (in the aquarium section) or online. Most of these kits involve either putting a few drops in the water or dipping in a testing paper and matching up colors. The cost for these kits can range from under $5 for aquarium testing strips to $150 for a high-end testing meter.
Looking at the data and what kids can do to make it better
The general range of pH for U.S. surface waters is about 6.5 to 8.5. The pH depends on many factors such as plants next to the stream, soils and rocks in the area, and the presence of water pollutants. In Texas, for example, the pH ranges from five to nine. Michigan soils tend to be high in calcium, which buffers lakes and streams from rapid changes in pH. Most Michigan water permits limit the discharge pH to 6.5 to nine to protect aquatic life. The current drinking water standard for pH is between 6.5 and 8.5.
If the pH is high (above eight), a common cause is some kind of soap or detergent discharge. It could be a nearby carwash, or a clothes washing machine that discharges to the stream. Wood ashes can also have a high pH, so if there has been burning near the stream site it could result in the pH being higher.
If the pH is low (below 6.5), there may be a long list with a range of reasons. Runoff from some fertilizers or acid rain input is a common culprit.
If you find a site with a high or low pH, going back to the site while testing upstream and downstream can help the students isolate the cause of the problem.
