Friday, October 18, 2013

Simulating the Effects of Acid Rain

Materials Required:
 - Bottle of Vinegar (1/2 cup per group)
- Chalk (two to three pieces per group)
- Zip lock bags (2 per group)
- Droppers (2 per group)
- Plates (2 per group)
- Tap water (1/2 cup per group) 

  • Place one piece of chalk in each pan.
  • Using the dropper drip vinegar onto the chalk on one of the plates in a constant stream.
  • Using the dropper drip water onto the chalk on the second plate in a constant stream. 
Scientific Explanation: 
Acid rain is caused mostly by the combustion of fossil fuels containing sulfur and nitrogen. When sulphur and nitrogen are combusted, sulphur dioxide and nitrogen oxides are created and released into the atmosphere. Once these gases come in contact with water they become acids (Sulphuric acid and Nitric acid). This can happen either through wet deposition when rain, sleet or snow remove the gases from the air or through dry deposition when particles are deposited and absorbed into surfaces and later converted into acids when they come into contact with water. Coal power plants, electricity generation, driving a car, volcanoes and thunderstorms all contribute to acid rain. While there are natural causes of acid rain as mentioned, 90% of harmful emissions are a result of man-made sources. Acidity of rainwater is measured by the pH scale. It ranges from 0 which is highly acidic to 14 which is highly alkaline (basic). The scale point 7 is neutral. Clean rain measures at pH 5.6 while acid rain is anything measuring between pH 5 and pH 0. Acid rain has an adverse effect on the natural environment including forests, freshwaters and soils. It not only kills insect and aquatic life forms but also causes damage to buildings and has impacts on human health. Acid rain destroys the surface of trees and depletes essential nutrients in the soil greatly impacting plant germination and reproduction, causing vulnerability to disease and stunting its growth. It increases the level of acidity in water sources which inhibits the ability for natural mechanisms to cope. Gradually the most fragile creatures and life forms begin to die. Lastly, acid rain damages buildings through corrosion and fracturing.

Great structures such as the Taj Mahal and the Washington Monument buildings have all suffered the harmful effects of acid rain. Buildings made of limestone are particularly impacted.
In order to mimic the effect of acid rain on the environment specifically on rock (limestone) we used vinegar and chalk. It may take a considerable amount of time to see the visible effects of acid rain yet the reaction of vinegar and chalk is instant and illustrates the same concept. The reaction of vinegar and chalk is an example of an acid- base reaction (neutralization). Vinegar, the acid, has a pH level of 3 while the chalk also known as calcium carbonate is a base at pH 8. When they are combined the chalk starts to bubble and foam up. The acid breaks apart the calcium carbonate and produces calcium and carbon dioxide gas. The bubbles you see during the reaction are carbon dioxide. On the surface of the vinegar are small pieces of chalk which have been neutralized.

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