Acid Rain and Table Salt: Chemistry and Environmental Impact
Acid Rain
Formation and Causes
Acid rain results from emissions of nitrogen oxides and sulfur oxides from factories, power plants, metallurgical industries, and vehicles burning fossil fuels like coal and petroleum.
Mechanism
Water from clouds reacts with these oxides to form sulfuric and nitric acid, resulting in acid rain with a pH of 3-5.
Border Phenomenon
Primary atmospheric contaminants can travel long distances, carried by winds for hundreds or thousands of miles before being deposited through mist, rain, drizzle, hail, snow, fog, or mist.
Consequences
- Lake Water Acidification: Lakes lack the self-purification capacity of rivers.
- Forest Damage: Yellowing of needles and subsequent massive drop.
- Soil Degradation: Kills nitrogen-fixing microorganisms, affecting soil fertility.
- Nutrient Depletion: Leaching of nutrients from the soil.
- Plant Stress: Plants become vulnerable to pests and require fertilizers and pesticides.
- Eutrophication: Leaching of nitrates and sulfates leads to excessive algae and aquatic plant growth.
- Erosion of Buildings and Statues: Dissolution of calcium carbonate causes a corroded appearance.
- Respiratory Problems: Aggravates chronic lung diseases, especially in the elderly and children.
- Increased Morbidity: Higher rates of lung diseases in children.
Solutions
- Emission Reduction: Requires environmental commitment from factories, but controls are not always effective.
- Promote Natural Gas Use
- Increase Use of Natural Gas Vehicles
- Protect Buildings and Statues: Use protective agents and consolidants to reinforce structures and provide hydrophobic properties.
Table Salt
Structure and Obtaining
Sodium chloride (table salt) is a white, crystalline solid at room temperature, soluble in water. Its structure consists of alternating sodium cations and chloride anions in a three-dimensional lattice. It’s found in oceans, seas, rivers, lakes, the mineral halite (rock salt), and salt deposits. The Dead Sea has the highest concentration (30%).
Origin of Name
The word “salt” comes from salarium, the payment Roman soldiers received in salt. In ancient times, salt was as valuable as gold and used as a condiment and preservative.
Past Uses
Before refrigeration, salt was used to preserve meat and other foods like fish, olives, onions, and cucumbers in brine.
Current Uses
Besides seasoning and preserving food, sodium chloride is used to produce bleach (sodium hypochlorite), antacids (sodium bicarbonate), caustic soda (sodium hydroxide), and muriatic acid (hydrochloric acid).
Importance for Consumers
Sodium chloride is essential for regulating fluid balance, kidney function, blood volume, and blood pressure.
Extraction from Salt Flats
Salt flats are vast, white expanses. Examples include La Colorada Grande (La Pampa) and Salinas Grandes (Jujuy).
Extraction Stages
- Drilling: Accessing brine at 70-80 cm depth.
- Purification: Settling in large pools.
- Evaporation: Sodium chloride crystals form at the edges of the pools.
- Collection: Crystals are gathered from the center.
- Drying: Using hot air currents.
- Additives: Starch or magnesium carbonate prevent clumping.
By National Law No. 17,259, iodine is added to salt at a 1:30,000 ratio to prevent endemic goiter and related mental retardation.
- Collection and Packaging
- Grinding: Producing different grain sizes for various uses.
Odor of the Sea
The characteristic sea smell comes from dimethyl sulfide (DMS), produced by microbes near plankton and marine plants. DMS contributes to cloud formation and helps seabirds locate food.