Precipitation reactions also play a central role in many chemical analysis techniques, including spot tests used to identify metal ions and gravimetric methods for determining the composition of matter (see the last module of this chapter). They are used widely in industry for production of a number of commodity and specialty chemicals. These reactions are common in nature and are responsible for the formation of coral reefs in ocean waters and kidney stones in animals. Many reactions of this type involve the exchange of ions between ionic compounds in aqueous solution and are sometimes referred to as double displacement, double replacement, or metathesis reactions. Precipitation Reactions and Solubility RulesĪ precipitation reaction is one in which dissolved substances react to form one (or more) solid products. The following sections of this chapter (section 6.2-6.4) will provide an introduction to three of the most prevalent types of chemical reactions: precipitation, acid-base, and oxidation-reduction. Faced with a wide range of varied interactions between chemical substances, scientists have likewise found it convenient (or even necessary) to classify chemical interactions by identifying common patterns of reactivity. When they exchange blows with their fists or feet, we say they are fighting. When two humans exchange information, we say they are communicating. Humans interact with one another in various and complex ways, and we classify these interactions according to common patterns of behavior. Predict the solubility of common inorganic compounds by using solubility rules.Recognize and identify examples of precipitation reactions.Next, learn about the Effects of Acid Rain.By the end of this section, you will be able to: The Long-Term Monitoring (LTM) Network measures and monitors surface water chemistry at over 280 sites to provide valuable information on aquatic ecosystem health and how water bodies respond to changes in acid-causing emissions and acid deposition. When acid deposition is washed into lakes and streams, it can cause some to turn acidic. Air concentrations are measured by CASTNET at more than 90 locations. Dry deposition estimates for nitrogen and sulfur pollutants are provided by the Clean Air Status and Trends Network (CASTNET). ![]() Unlike wet deposition, dry deposition is difficult and expensive to measure. The NADP/NTN collects acid rain at more than 250 monitoring sites throughout the US, Canada, Alaska, Hawaii and the US Virgin Islands. Policymakers, research scientists, ecologists, and modelers rely on the National Atmospheric Deposition Program’s (NADP) National Trends Network (NTN) for measurements of wet deposition. Acid rain usually has a pH between 4.2 and 4.4. Normal rain has a pH of about 5.6 it is slightly acidic because carbon dioxide (CO 2) dissolves into it forming weak carbonic acid. ![]() The lower a substance's pH (less than 7), the more acidic it is the higher a substance's pH (greater than 7), the more alkaline it is. For example, in desert areas the ratio of dry to wet deposition is higher than an area that receives several inches of rain each year.Īcidity and alkalinity are measured using a pH scale for which 7.0 is neutral. The amount of acidity in the atmosphere that deposits to earth through dry deposition depends on the amount of rainfall an area receives. When the accumulated acids are washed off a surface by the next rain, this acidic water flows over and through the ground, and can harm plants and wildlife, such as insects and fish. The acidic particles and gases may deposit to surfaces (water bodies, vegetation, buildings) quickly or may react during atmospheric transport to form larger particles that can be harmful to human health. ![]() Dry DepositionĪcidic particles and gases can also deposit from the atmosphere in the absence of moisture as dry deposition. The sulfuric and nitric acids formed in the atmosphere fall to the ground mixed with rain, snow, fog, or hail. Wet deposition is what we most commonly think of as acid rain. Winds can blow SO 2 and NO X over long distances and across borders making acid rain a problem for everyone and not just those who live close to these sources. Manufacturing, oil refineries and other industries.Two thirds of SO 2 and one fourth of NO X in the atmosphere come from electric power generators. Burning of fossil fuels to generate electricity.The major sources of SO 2 and NO X in the atmosphere are: While a small portion of the SO 2 and NO X that cause acid rain is from natural sources such as volcanoes, most of it comes from the burning of fossil fuels. These then mix with water and other materials before falling to the ground. The SO 2 and NO X react with water, oxygen and other chemicals to form sulfuric and nitric acids. Acid rain results when sulfur dioxide (SO 2) and nitrogen oxides (NO X) are emitted into the atmosphere and transported by wind and air currents.
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