Acid Rain

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Acid Rain Acid rain has become an environmental concern within the last decade. The increasing environmental awareness of the poor condition of planet earth has not lessened the concern about acid rain.

What is acid rain? Acid rain is rain with pH values of less than 5.6. Acid rain is rain mixed with sulfur. Sulfur is put into the air by sulfuric acid plants. Some of the larger sulfuric acid plants are in Ontario Canada Where dose acid rain come from? There are several factors decide the location of each manufacturing plant. Some of these factors are: 1. Is there ready access to raw materials? 2. Is the location close to major transportation routes? 3. Is there a suitable work force in the area for plant construction and operation? 4. Is there sufficient energy resources readily available? 5. Can the chemical plant can carry out its operation without any unacceptable damage to the environment? The following will explain in greater detail why these factors should be considered.

1) Raw Materials: The plant needs to be close to the raw materials that are used in the production of sulfuric acid like sulfur, lead, copper, zinc and sulfides.

2) Transportation: A manufacturer must consider transportation routes. The raw materials have to be transported to the plant, and the final product must be transported to the consumer or distributor. Commission proof container are required for the transportation of sulfuric acid while sulfur can be much more easily transported by truck or train.

3) Human Resources: For a sulfuric acid plant to operate, a large work force will be required to run the plant. The plant must employ chemists, technicians, administrators, computer operators, and people in sales and marketing.

4) Energy: Large amounts of energy will be required. Distance to a plentiful supply of energy is often a determining factor in deciding the plant's location.

5) Environmental Concerns: Concerns about the environment must be carefully taken into consideration. The chemical reaction of changing sulfur and other substances to sulfuric acid results in the creation of other substances like sulfur dioxide. This causes acid rain.

6) Water Supplies: Another question is the closeness of the location of the plants water supply since large amounts of water will be needed for cooling.

Producing Sulfuric Acid Sulfuric acid is produced by two processes-the chamber process and the contact process.

The contact process is the current process being used to produce sulfuric acid. In the contact process, a purified dry gas mixture containing 7-10% sulfur dioxide and 11-14% oxygen is passed through a preheater to a steel reactor containing a platinum or vanadium peroxide catalyst. The catalyst promotes the oxidation of sulfur dioxide to trioxide. This then reacts with water to produce sulfuric acid. In practice, sulfur trioxide reacts not with pure water but with recycled sulfuric acid. The reactions are: 2SO2 + O2 > 2SO3 SO3 + H2O > H2SO4 The product of the contact plants is 98-100% acid. This can either be diluted to lower concentrations or made stronger with sulfur trioxide to yield oleums. For the process, the sources of sulfur dioxide may be produced from pure sulfur, from pyrite, taken from smelter operations or by oxidation of hydrogen sulfide recovered from the purification of water gas, refinery gas, natural gas and other fuels. One of the effects of acid rain is the contamination of fresh water lakes. Lets consider the following scenario, a lake is contaminated by acid rain how do you neutralize it.

i) The concentration of sulfuric acid is 0.0443 mol/L.

The pH is: No. Mol of hydrogen ions = 0.0443 mol/L x 2 = 0.0886 mol/L hydrogen ions pH = - log [H] = - log (0.0886) = - (-1.0525) = 1.05 Therefore, pH is 1.05.

ii) The amount of base needed to neutralize the lake water is: volume of lake = 2000m x 800m x 50m = 800,000,000 m3 or 8x108 m3 since 1m3=1000L, therefore 8x1011 L 0.0443 mol/L x 8x1011 = 3.54 x 1010 mol of H2SO4 in water # mol NaOH = 3.54 x 1010 mol H2SO4 x 2 mol NaOH 1 mol H2SO4 = 7.08 x 1010 mol of NaOH needed Mass of NaOH = 7.08 x 1010 mol NaOH x 40 g NaOH 1 mol NaOH = 2.83 x 1012 g NaOH or 2.83 x 109 kg NaOH Therefore a total of 2.83 x 1012 g of NaOH is needed to neutralize the lake water.

iii) The use of sodium hydroxide versus limestone to neutralize the lake water: Sodium hydroxide: Sodium hydroxide produces water when reacting with an acid; it also dissolves in water very easily. When using sodium hydroxide to neutralize a lake, there may be several problems. One problem is that when sodium hydroxide dissolves in water, it gives off heat and this may harm aquatic living animals.

Limestone: Is another way to neutralize a lake. Liming of lakes must be done with considerable caution and with an awareness that the underwater ecosystem will not be restored to its original pre-acidic state even though the pH of water may have returned to more normal levels. When limestone dissolves in water it produces carbon dioxide. This could be a problem since a higher content of carbon dioxide would mean a lowered oxygen content especially when much algae growth is present. As a result, fish and other underwater animals may suffer. Limestone also does not dissolve as easily as sodium hydroxide taking a longer period of time to react with sulfuric acid to neutralize the lake. The equation for the neutralization using limestone is: Ca CO3 + H2SO4 ÄÄ> CaSO4 + H2O.

In conclusion there are also many other sources of sulfur that contribute to acid rain such as power plants, steel mills and automobiles. Although these emissions need to be controlled they are not major contributers. There are many opposing views as to the causes of acid rain and the best way to control it. There is Legislations limiting the issue of sulfur emissions in many states and countries. There are also many ideas on ways to clean the emissions. All of this has been very costly to the people of our planet both economically and environmentally and we are still not able to effectively control acid rain. Until everyone works together to control acid rain the efforts of a few countries will not stop the effects of acid rain