Acid Rain

 

Chemist Questions by Brianna C.

What is Acid Rain?

The term "acid rain" is commonly used to mean the depostition of acidic components in rain, snow, fog, dew, or dry particles. The more accurate term is "acid precipitation". Acid precipitation has a pH of anything below 5.6.

What chemicals make rain acidic, and how does it happen?

The extra acidity in rain comes from the reaction of air pollutants; primarily sulfur oxides and nitrogen oxides, with water in the air to form strong acids (like sulfuric and nitric acid). The main sources of these pollutants are vehicles and industrial and power-generating plants.

Where do these chemicals come from?

The main local sources are cars, trucks, and buses. Also, the chemicals come from pollutants from factories.
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How do we measure the acidity of rain?

Acidity in rain is measured by collecting samples of rain and meausring its pH. To find the distribution of rain acidity, weather conditions are monitored and rain samples are collected at different locations all over the country. The areas of greatest acidity (lowest pH values) are located in the Northeastern United States. The large number of cities, the dense population, and the concentration of power and industrial plants in the Northeast cause the pattern of high acidity. In addition, the prevailing wind direction brings storms and pollution to the Northeast from the Midwest, and dust from the soil and rocks in the Northeastern United States is less likely to neutralize acidity in the rain.

What is pH?

It is the measure of acidity or alkalitinty of a solution. If the solution is 7, than it is neutral. The normal scale ranges from 0 to 14 and the lower you go, the more acidic the solution is. On the other hand, the higher you go, the more alkaline the solution is.

 Describe the pH range and list various things that correspond to the various pH levels.

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Liquids with a pH less than 7 are acid, and those with a pH greater than 7 are alkaline (or basic). If a solution has a pH of exactly 7, like water, it is neutral. Here is a list of some common household items: 
1.0 battery acid (sulfuric acid)
2.2-2.4 lemon juice
2.2 vinegar (acetic acid)  
2.9-3.3 apple juice
4.0-4.5 tomatoes
5.6 unpolluted rain
6.4 cow's milk
7.0 distilled water
7.3-7.5 human blood
8.1 average seawater
8.3 baking soda
10.5 milk of magnesia
12.0 ammonia
13.0 lye

What is the pH of normal rain, and at what level does the pH become dangerous?

'Normal' or 'unpolluted' rainfall has a pH of 5.6. This is slightly acidic due to the presence of carbon dioxide in the atmosphere, which forms weak carbonic acid in water. It is not uncommon for acidified rainwater to have a pH of 4, about 30 times as acidic as normal rainwater. When the pH of rain gets anywhere under 5.6, that is when it starts to become dangerous.