Outdoor Classroom
Curriculum Overview

physics

biology

chemistry

hydrology

local lessons
for West Philadelphia

links and references

 pH and buffering
Materials

pH paper or tester kit (purchase in a pet fish store or at a school supplier)

Theory pH is defined as -log[H+]. If [H+] is 10E-7, then the pH is 7. To skip math, use examples to teacr what pH means. The theoretical range of pH is about -2 (pure acid) to 26. The natural range of pH is about 1 (acid mine drainage in Colorado or British Columbia) to 8 or 9 in very alkaline (salty) lakes such as Great Salt Lake, Utah. The ocean is about 8.3. Your stomach is about 4. Pure water is about 5.5. Healthy rivers and lakes are usually 6 to 7. What affects pH of lakes and rivers? Often, it's what the riverbed or lake watershed is made of. If it's made of rocks that dissolve easily, the pH goes up, and the dissolved rocks buffer the lakes and rivers against pH changes. This is analogous to taking antacids such as calcium tablets to help an upset stomach. An upset stomach has too much stomach acid, which burns your stomach liner and other parts. The antacid (anti-acid) is chalk (calcium carbonate), a type of rock which neutralizes the acid and raises the pH of your stomach to some level less painful. Rocks dissolved more slowly (over years) act as antacids for lakes. Too much acid (or not enough buffering capacity) can cause an upset lake. Fish and microorganisms suffer when pH levels fall below 5.
Use Dip the pH paper (or the vial) in the water quickly. Compare the colors to those on the packaging. Note pH.
Suggested Lesson What is the pH of your local water body? Is it high, or low? What are the surroundings of this water? Do you think that the water is well buffered, or not very buffered?
Extra Credit  
History The pH levels of lakes in the Northeast area of the US became dangerously low in the 80's and 90's because of sulfur and nitrogen oxide burning byproducts industrial and car exhaust. Sulfur and nitrogen oxides react quickly with water in the atmosphere to make sulphuric acid and nitric acid. These very strong acids travel with clouds from the industries and cars in the Midwestern US and fall with the rain onto the lakes of the Adirondacks mountain range in New York. Fish could not survive in the low pH water. Because the mountain lakes were not well buffered (they didn't have a lot of dissolved rock in them), they were particularly vulnerable to acid rain.



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