Overview:
Acid rain- the falling of acids and acid forming compounds from the atmosphere to the earth's surface.
As sulfur dioxide and nitrogen oxides are transported as much as 600 miles by winds, they form secondary pollutants such as nitric acid vapor, droplets of sulfuric acid and particles of sulfate and nitrate salts. These chemicals descend to the earth's surface in two forms;
- Wet- as acid rain, snow fog and cloud vapor
- Dry- as acidic particles.
The resulting mixture is called acid deposition, commonly called acid rain.
Acidity of substance in water is commonly expressed in terms of pH, with pH values greater than 7 (alkaline) and pH values less than 7 being acidic.
Acid deposition has many harmful effects, especially when the pH fall below 5.1 for terrestrial systems and below 5.5 for aquatic system. It contribute to human respiratory disease such as bronchitis and asthma, which can cause premature death and it damages statues, buildings, and metal of car finishes. It can release from soil, soluble aluminum ions that when washed into lakes can kill many kind of fish by stimulating mucous formation, which clogs the fishes gills. Excess acidity can contaminate fish in some lakes.
Activities
Project 1. Acid rain in the local environment:
Materials:
- pHydrion paper(pH)
- Rain water
Procedure:
Have students collect rain samples from their different neighborhoods or from different time periods. Bring the samples to class to measure the pH using pH paper. Compare the pH values from the different neighborhoods. Chart the results. *Remember to place names and locations on the water sample.
Hypothesize why results may be different from one neighborhood to another or at different time periods ( right after rain starts, after more than one day of rain etc.).
Project 2:
Compare the pH values in several other solutions such as vinegar, apple juice, lemon juice, tomato juice, dissolved alka seltzer and baking soda.Have the students neutralize these solutions.If possible have the students quanitify how much acid or base is required to neutralize each solution.
Have the students compare the acidity of lemon or tomato juice with actual pH recorded over areas in the US.
Project 3:
Acid Rain and it's impact on vegetation: Supply students with seeds of various rapidly germinating species: ie. radish ( early scarlet globe); alfalfa, green beans, cucumbers, mustard all germinate within 3-7 days.
Have students position 10-25 seeds of each type in four separate petri dishes on top of filter paper.Gently water or moisten ( approximately 2-5 ml) each plate with one of the sterile pH water sources; the solutions should range in pH from 3 up to 10 depending on your resources.
Starting on day 3 and every day thereafter, have the students record the percentage of seeds germinating, and if time permits, measure the length of the roots and shoot by pH treatment.At the end of 10 days, have them graph the results.
Potential discussion questions might include if all species are impacted the same, how acid rain influences root morphology, and if possible how acid rain alters the ions that plants 'pick' up from soil.
Project 4: Effect of acid rain on buildings, monuments and other objects ( modified from Science Experiments for K-12 Teachers listed below)
OBJECTIVE: To demonstrate chemical weathering brought about by acid rain. Chalk is representative of a calcite building material such as limestone, and vinegar (or other acidic solutions) represent acid rain.
Equipment