Measuring pH

Background

What substances are acidic or alkaline? The measure of hydrogen ions (H+) in a solution is called the pH. A solution is more acidic when it contains more hydrogen ions. PH is measured on a scale of 0-14, where 0 is extremely acidic, 7 is neutral, and 14 are extremely basic.
Several factors contribute to the natural pH level of water and soils. For example, vegetation type and density, the underlying strata of rocks and soil, and the quality of water flowing through the area will affect ground water and soil acidity. The pH range of natural systems under normal circumstances is usually between 6.0 and 8.0. This is the normal range, but some plants can tolerate harsher conditions. Some of the plants and animals of highly - acidic peat bogs can tolerate these severe environments. The pH level of the water in wetlands is important to plants and animal life. The sudden dramatic change in pH could endanger the lives of young animals, in particular.
Humans can also change the level of acidity on watery environments. Air pollution from automobiles and coal burning utilities and factories contribute to acid rain. Sulfur dioxide (SO2) and nitrogen oxide (NO2) are emitted from tailpipes and smokestacks. When these compounds combine with water in the atmosphere, they form sulfuric and nitric acids (H2 SO4 and HN3 ) which fall to the earth as acid rain, snow, hail and fog. This precipitation mixes with surface water in creeks, ponds, rivers and wetlands.
Other pollutants transported in runoff can also change the acidity of the water in wetlands. On the other hand, the lime in agricultural and household products has an opposite, buffering or neutralizing effect. When limestone combines with water that has a pH less than 8.0, it reduces acidity. In general, naturally occurring organic acids from plants (sphagnum moss, several tree species, etc.) are weaker and less harmful to life than inorganic acids, such as sulfuric acid. In fact, organic acids from plants can actually have a buffering effect on the inorganic acids that may have entered the system.

Materials

• Small jars or cups
• vinegar
• milk
• lemon juice
• ammonia
• tap water
• distilled water
• soda pop
• chalk
• baking soda
• aspirin
• antacid tablets
• safety goggles
• broom handle
• wire or string

Procedure

1. Test and compare some common substances from the list using pH paper. Draw a pH scale and use it to compare the results of each test. Distilled water has a pH of 7; lemon juice, pH 2; vinegar, pH 3.5; natural rainfall, pH 5.6; baking soda pH 8; ammonia: pH 12.
   
2. A buffer is something that neutralizes acids and bases in solutions. Chalk (calcium carbonate, CaCO3), baking Soda, (NaHCO3), and antacids act as buffers. Mix these with lemon juice and vinegar and test again. Wear goggles for this and don’t mix anything with the ammonia.
   
3. Rinse a jar with distilled water and place it outside to collect rainwater. Check to see if the rainwater is more acidic or neutral.
   
4. At a wetland site, collect small water samples from several locations and measure the pH. To sample water beyond your reach; use the string or wire to attach the jar to the broomstick for collecting.
   

• How does the pH of the wetland compare to the pH of the rainwater?
  
• Do you think the rain has any effect on the wetland water? If possible test the pH of the water right after it rains.
  
• Are other factors affecting the pH of the water? Was the pH taken along the shore different from the other measurements?
  
• Get a GPS reading at each site from which you collect data.
  

Of course, the data collected from the GPs will not differentiate how far from the shore you tested the water, so indicate that information on your data collection sheet.