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Neutralization
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The Gale Encyclopedia of Science, 2014
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In chemistry, the process in which an acid and a base react with each other to form a salt and water is known as neutralization. Just as a neutral color contains no vivid colors and a neutral person has no strong opinions, a neutralization reaction between an acidic and a basic (alkaline) solution lessens the acidic and basic properties of both solutions. Taking an antacid to settle a sour stomach, putting agricultural limestone on a garden or lawn, and mixing baking soda with vinegar are everyday examples of neutralization reactions.
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History As acids and bases are readily found in nature, neutralization reactions have been biological occurrences since ancient times. For instance, neutralization reactions involving carbonate and bicarbonate regulate the pH of our blood. However, fundamental understanding of neutralizations began with Svante Arrhenius (1859-1927) in 1884 and Johannes Brønsted (1879-1947) and Thomas Lowry (1874-1936) in 1923. These people first articulated the chemical properties of acids and bases and how the two substances react in water to form salts. Brønsted and Lowry defined acids as hydrogenproton donors and bases as hydrogen proton acceptors. The Brønsted-Lowry definition is best understood and most used by chemistry students. Gilbert Lewis's (1875-1946) definition of acids and bases, also published in 1923, is useful when substances do not contain or receive hydrogens.
Table of Contents History Reactions Uses of neutralization
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Reactions All neutralization reactions can be broadly summarized by the following equation: acid + base Õ salt + water Using a hydrogen ion to represent an acid and a hydroxide ion to represent a base, a neutralization reaction may also be expressed as
Related Subjects Acids Antacids Arrhenius, Svante Bases (Chemistry) The formation of the salt is omitted in this generalized type of equation because the salt ions do not undergo a chemical change during a neutralization reaction. Neutralization reactions usually take place in water. An example of a strong acid and a strong base reacting in water-indicated by (aq), meaning aqueous-is the reaction between two corrosive solutions, sodium hydroxide (NaOH) and hydrochloric acid (HCl), to form table salt (NaCl) and water. The table salt remains dissolved in the water and exists as ions of sodium (Na+) and chloride (Cl−).
Neutralization does not occur only in solution. Acidic and basic gases can undergo neutralization reactions, as in the reaction between the two corrosive gases ammonia (NH3) and hydrogen chloride (HCl) to form the solid salt ammonium chloride (NH4Cl).
Weak acids and bases will also undergo neutralization reactions. The reaction of the acetic acid (HAc) in vinegar with the sodium bicarbonate (NaHCO3) in baking soda produces water, sodium ions (Na+), acetate ions (Ac−), and carbon dioxide gas (CO2). The reaction between baking soda and acids in dough creates bubbles of carbon dioxide that make cakes and cookies rise and become fluffy.
Uses of neutralization Neutralization of acidic water is an important step in reclaiming land that was once mined. Mine run-off renders water around the mine site acidic, and the acid must be neutralized with lime, or calcium oxide (CaO) acting as a base, before the area can be reclaimed. However, this procedure is expensive. Recent studies have shown that constructed wetlands—human-made shallow ponds containing water plants such as cattails—can be an effective and less costly method of neutralizing acid mine drainage. Neutralization of soil is sometimes necessary in order to promote plant growth. The ability of plants to take nutrients from the soil into their roots is affected by the pH content of the surrounding soil particles. Acid rain can cause soil to become acidic. Some plants benefit from liming the soil. In the liming process, agricultural limestone-calcium carbonate (CaCO3) that may also contain magnesium carbonate (MgCO3) neutralizes acid in the soil and provides nutrients to promote plant growth. Since liming can stimulate plant growth, it is important to also fertilize limed soil. This insures that all of the nutrients used by the plants for growth are maintained in the soil for the following year's growth. Soils may also become too basic, or alkaline, especially in areas where there is little precipitation. Substances that can act as acids such as calcium sulfate, also called gypsum (CaSO4), and sulfur (S2) can be applied to the soil for neutralization. In areas where acid precipitation is a problem, neutralization reactions can damage limestone, marble, and plaster buildings and statues. These structures all are made of calcium carbonate (CaCO3), a basic substance that is neutralized by acidic precipitation. These structures decay and become coated with a black substance that contains gypsum. Gypsum is the salt calcium sulfate (CaSO4) that is formed when the sulfuric acid (H2S) in acid rain reacts with the calcium carbonate (CaCO3) in the building materials.
KEY TERMS Acid A chemical substance that donates a hydrogen proton when it reacts with a base. Acid precipitation Rain, fog, sleet, or snow that has a lower pH than normal rain due to atmospheric pollutants; sometimes called acid rain. Base A substance that receives a hydrogen proton when it reacts with an acid. Ion An atom or molecule which has acquired electrical charge by either losing electrons (positively charged ion) or gaining electrons (negatively charged ion). pH A logarithmic scale that expresses the concentration of hydrogen ions in a solution of water. A neutral solution with equivalent amounts of hydrogen and hydroxyl ions has a pH of 7.0 at room temperature. Acidic solutions have a pH of less than 7.0 and basic (alkaline) solutions have a pH of more than 7.0. Salt A solid that is made from a combination of positive and negative ions but has no net charge itself. Titration A process in which a carefully measured amount of a wellcharacterized chemical substance is added to a substance of unknown concentration until a complete reaction has occurred. Titrations are used for chemical analyses. Acidic and basic hazardous wastes can often be safely disposed of using neutralization because the salts produced are usually non-hazardous and take up less space as solids than the liquid acids and bases.
Further Readings Books Brown, Theodore, H. Eugene LeMay, and Bruce E. Bursten. Chemistry: The Central Science, 10th ed. Upper Saddle River, NJ: Prentice Hall, 2005. Troeh, Fredrick R. and Louis M. Thompson. Soils and Soil Fertility . 6th ed. New York: Oxford University Press, Inc., 2005.
Periodicals Cardinall, Mario Emilio, Claudio Giomini and Giancarlo Marrosu. “More about the Extent of Acid-Base Reactions.” Journal of Chemical Education Vol. 68, no. 12, 1991, pp. 989-990. Full Text: COPYRIGHT 2014 Gale, Cengage Learning.
Source Citation Haustein, Catherine Hinga. "Neutralization." The Gale Encyclopedia of Science, edited by K. Lee Lerner and Brenda Wilmoth Lerner, 5th ed., Gale, 2014. Science in Context, http://link.galegroup.com/apps/doc/CV2644031529/SCIC?u=dc_demo&xid=a92440c6. Accessed 11 Mar. 2018. Gale Document Number: GALE|CV2644031529
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