Editing Acid (section)

==Applications of acids==

===In industry===
Acids are fundamental reagents in treating almost all processes in modern industry. Sulfuric acid, a diprotic acid, is the most widely used acid in industry, and is also the most-produced industrial chemical in the world. It is mainly used in producing fertilizer, detergent, batteries and dyes, as well as used in processing many products such like removing impurities.<ref>{{Cite web|title = The Top 10 Industrial Chemicals - For Dummies|url = http://www.dummies.com/how-to/content/the-top-10-industrial-chemicals.html|website = dummies.com|access-date = 2016-02-05}}</ref> According to the statistics data in 2011, the annual production of sulfuric acid was around 200 million tonnes in the world.<ref>{{Cite web|title = Sulfuric acid|url = http://www.essentialchemicalindustry.org/chemicals/sulfuric-acid.html|website = essentialchemicalindustry.org|access-date = 2016-02-06}}</ref> For example, phosphate minerals react with sulfuric acid to produce [[phosphoric acid]] for the production of phosphate fertilizers, and [[zinc]] is produced by dissolving zinc oxide into sulfuric acid, purifying the solution and electrowinning.

In the chemical industry, acids react in neutralization reactions to produce salts. For example, [[nitric acid]] reacts with [[ammonia]] to produce [[ammonium nitrate]], a fertilizer. Additionally, [[carboxylic acid]]s can be [[Esterification|esterified]] with alcohols, to produce [[ester]]s.

Acids are often used to remove rust and other corrosion from metals in a process known as [[pickling (metal)|pickling]]. They may be used as an electrolyte in a [[wet cell battery]], such as [[sulfuric acid]] in a [[car battery]].

===In food===
[[File:Tumbler of cola with ice.jpg|thumb|Carbonated water (H<sub>2</sub>CO<sub>3</sub> aqueous solution) is commonly added to soft drinks to make them effervesce.]]
[[Tartaric acid]] is an important component of some commonly used foods like unripened mangoes and tamarind. Natural fruits and vegetables also contain acids. [[Citric acid]] is present in oranges, lemon and other citrus fruits. [[Oxalic acid]] is present in tomatoes, spinach, and especially in [[carambola]] and [[rhubarb]]; rhubarb leaves and unripe carambolas are toxic because of high concentrations of oxalic acid. [[Ascorbic acid]] (Vitamin C) is an essential vitamin for the human body and is present in such foods as amla ([[Phyllanthus emblica|Indian gooseberry]]), lemon, citrus fruits, and guava.

Many acids can be found in various kinds of food as additives, as they alter their taste and serve as preservatives. [[Phosphoric acid]], for example, is a component of [[cola]] drinks. [[Acetic acid]] is used in day-to-day life as vinegar. Citric acid is used as a preservative in sauces and pickles.

[[Carbonic acid]] is one of the most common acid additives that are widely added in [[soft drink]]s. During the manufacturing process, CO<sub>2</sub> is usually pressurized to dissolve in these drinks to generate carbonic acid. Carbonic acid is very unstable and tends to decompose into water and CO<sub>2</sub> at room temperature and pressure. Therefore, when bottles or cans of these kinds of soft drinks are opened, the soft drinks fizz and effervesce as CO<sub>2</sub> bubbles come out.<ref>{{Citation|title = Method of and apparatus for making and dispensing a carbonated beverage utilizing propellant carbon dioxide gas for carbonating|url = https://patents.google.com/patent/US4304736|date = 8 December 1981|access-date = 2016-02-06|first1 = John R.|last1 = McMillin|first2 = Gene A.|last2 = Tracy|first3 = William A.|last3 = Harvill| first4 = William S. Jr. |last4 = Credle}}</ref>

Certain acids are used as drugs. [[Acetylsalicylic acid]] (Aspirin) is used as a pain killer and for bringing down fevers.

===In human bodies===
Acids play important roles in the human body. The hydrochloric acid present in the stomach aids digestion by breaking down large and complex food molecules. Amino acids are required for synthesis of proteins required for growth and repair of body tissues. Fatty acids are also required for growth and repair of body tissues. Nucleic acids are important for the manufacturing of DNA and RNA and transmitting of traits to offspring through genes. Carbonic acid is important for maintenance of pH equilibrium in the body.

Human bodies contain a variety of organic and inorganic compounds, among those [[dicarboxylic acid]]s play an essential role in many biological behaviors. Many of those acids are [[amino acids]], which mainly serve as materials for the synthesis of proteins.<ref>{{Cite book|title = 8 - Biological roles of amino acids and peptides - University Publishing Online|url = http://ebooks.cambridge.org/chapter.jsf?bid=CBO9781139163828&cid=CBO9781139163828A114|archive-url = https://web.archive.org/web/20160302214930/http://ebooks.cambridge.org/chapter.jsf?bid=CBO9781139163828&cid=CBO9781139163828A114|url-status = dead|archive-date = 2 March 2016|date = June 2012|doi = 10.1017/CBO9781139163828|last1 = Barrett|first1 = G. C.|last2 = Elmore|first2 = D. T.|isbn = 9780521462921}}</ref> Other weak acids serve as buffers with their conjugate bases to keep the body's pH from undergoing large scale changes that would be harmful to cells.<ref>{{Cite web|url = http://fitsweb.uchc.edu/student/selectives/TimurGraham/Acid_Buffering.html|title = Acid Buffering|year = 2006|access-date = 2016-02-06|website = Acid Base Online Tutorial|publisher = University of Connecticut|last = Graham|first = Timur|archive-url = https://web.archive.org/web/20160213132105/http://fitsweb.uchc.edu/student/selectives/TimurGraham/Acid_Buffering.html|archive-date = 13 February 2016|url-status = dead}}</ref> The rest of the dicarboxylic acids also participate in the synthesis of various biologically important compounds in human bodies.

===Acid catalysis===
{{Main|Acid catalysis}}
Acids are used as [[catalyst]]s in industrial and organic chemistry; for example, [[sulfuric acid]] is used in very large quantities in the [[alkylation]] process to produce gasoline.  Some acids, such as sulfuric, phosphoric, and hydrochloric acids, also effect [[Dehydration reaction|dehydration]] and [[condensation reaction]]s. In biochemistry, many [[enzyme]]s employ acid catalysis.<ref name="Voet acid cat">{{cite book |author=Voet, Judith G.|author2=Voet, Donald |title=Biochemistry |url=https://archive.org/details/biochemistry00voet_1|url-access=registration|publisher=J. Wiley & Sons |location=New York |date=2004 |pages=[https://archive.org/details/biochemistry00voet_1/page/496 496–500] |isbn=978-0-471-19350-0 }}</ref>