{"id":4398,"date":"2019-06-17T18:13:46","date_gmt":"2019-06-17T18:13:46","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/3-12-acids-and-bases-3\/"},"modified":"2023-11-30T17:51:40","modified_gmt":"2023-11-30T17:51:40","slug":"3-12-acids-and-bases-3","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/3-12-acids-and-bases-3\/","title":{"raw":"3.12 Acids and Bases","rendered":"3.12 Acids and Bases"},"content":{"raw":"
\r\n\r\n[caption id=\"attachment_1179\" align=\"alignright\" width=\"165\"]\"Image Figure 3.12.1. Batteries contain strong acids which should not come into contact with skin or eyes.<\/em>[\/caption]\r\n\r\n \r\n

Danger!\u00a0 Acid!<\/h1>\r\n<\/div>\r\nYou probably know that\u00a0\u00a0batteries\u00a0contain dangerous chemicals,\u00a0including\u00a0strong [pb_glossary id=\"1183\"]acids[\/pb_glossary]. Strong acids can hurt you if they come into contact with your skin or\u00a0eyes. Therefore, it may surprise you to learn that your life\u00a0depends<\/em>\u00a0on acids. There are many acids inside your body, and some of them are as strong as battery\u00a0acid. Acids are needed for\u00a0digestion and some\u00a0forms of [pb_glossary id=\"5753\"]energy[\/pb_glossary]\u00a0production. Genes are made of\u00a0[pb_glossary id=\"5475\"]nucleic acids[\/pb_glossary],\u00a0proteins\u00a0of\u00a0[pb_glossary id=\"5707\"]amino acids[\/pb_glossary], and\u00a0lipids\u00a0of [pb_glossary id=\"5657\"]fatty acids[\/pb_glossary].\r\n
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Water\u00a0and\u00a0Solutions<\/h1>\r\n<\/div>\r\nAcids (such as battery acid) are\u00a0solutions. A\u00a0[pb_glossary id=\"5811\"]solution[\/pb_glossary]<\/strong>\u00a0is a\u00a0mixture\u00a0of two or more substances that has the same\u00a0composition\u00a0throughout. Many solutions are a mixture of\u00a0water\u00a0and some other substance. Not all solutions are acids. Some are bases and some are neither acids nor bases. To understand acids and bases, you need to know more about pure water.\r\n\r\nIn pure\u00a0water\u00a0(such as distilled water), a tiny fraction of water molecules naturally breaks down to form ions. An\u00a0ion\u00a0is an electrically charged\u00a0atom or molecule. The breakdown of water is represented by the chemical equation:\r\n\r\n2 H2<\/sub>O \u2192 H3<\/sub>O<\/span>+<\/sup>\u00a0+ OH<\/span>-<\/sup>\r\n\r\nThe products of this reaction are a hydronium\u00a0ion\u00a0(H3O+<\/sup><\/span>) and a hydroxide\u00a0ion\u00a0(OH-<\/sup><\/span>). The hydroxide ion, which has a negative charge, forms when a water molecule gives up a positively charged hydrogen ion (H+<\/sup><\/span>). The [pb_glossary id=\"5771\"]hydronium ion[\/pb_glossary], which has a positive charge, forms when another water molecule accepts the hydrogen ion.\r\n
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Acidity and\u00a0pH<\/h1>\r\n<\/div>\r\nThe\u00a0concentration\u00a0of hydronium ions in a\u00a0solution\u00a0is known as\u00a0[pb_glossary id=\"5467\"]acidity[\/pb_glossary].<\/strong>\u00a0In pure water, the\u00a0concentration\u00a0of hydronium ions is very low; only about one in ten million water molecules naturally breaks down to form a hydronium ion. As a result, pure water is essentially neutral. [pb_glossary id=\"5467\"]Acidity[\/pb_glossary] is measured on a scale called\u00a0[pb_glossary id=\"5801\"]pH[\/pb_glossary]<\/strong>, as shown in Figure 3.12.2. Pure water has a pH of 7, so the point of neutrality on the pH scale is 7.\r\n\r\n[caption id=\"attachment_1196\" align=\"aligncenter\" width=\"600\"]\"Image Figure 3.12.2. The pH scale measures acidity. It ranges from 1-14.<\/em>[\/caption]\r\n\r\n
\r\n\r\nThis pH scale shows the acidity of many common substances. The lower the pH value, the more [pb_glossary id=\"5691\"]acidic[\/pb_glossary] a substance is.\r\n\r\n[caption id=\"attachment_2303\" align=\"aligncenter\" width=\"472\"]\"Image Figure 3.12.3. Examples of solutions for various pH levels.<\/em>[\/caption]\r\n\r\n<\/div>\r\n

Acids<\/h2>\r\nIf a\u00a0solution\u00a0has a higher\u00a0concentration\u00a0of [pb_glossary id=\"5771\"]hydronium ion[\/pb_glossary]s than pure water, it has a pH lower than 7. A solution with a pH lower than 7 is called an\u00a0[pb_glossary id=\"1183\"]acid[\/pb_glossary]<\/strong>. As the hydronium ion concentration increases, the pH value decreases. Therefore, the more acidic a solution is, the lower its pH value is.\r\n\r\nDid you ever taste vinegar? Like other acids, it tastes sour. Stronger acids can be harmful to organisms.\u00a0Even stomach\u00a0acid\u00a0would eat through the stomach if it were not lined with a layer of mucus. Strong acids can also damage materials, even hard materials such as glass.\r\n

Bases<\/h2>\r\nIf a solution has a lower concentration of hydronium ions than pure water, it has a pH higher than 7. A solution with a pH higher than 7 is called a\u00a0[pb_glossary id=\"5715\"]base[\/pb_glossary]<\/strong>. Bases, such as baking soda, have a bitter taste. Like strong acids, strong bases can harm organisms and damage materials. For example, lye can burn the skin, and bleach can remove the colour from clothing.\r\n
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Buffers<\/h1>\r\nA [pb_glossary id=\"9082\"]buffer[\/pb_glossary] is a solution that can resist changes in pH.\u00a0 Buffers are able to maintain a certain pH by by absorbing any H+ or OH- ions added to the solution.\u00a0 Buffers are extremely important in biological systems in order to maintain a pH conducive to life.\u00a0 Bicarbonate is an example of a buffer which is used to maintain pH of the blood.\u00a0 In this buffering system, if blood becomes too acidic, carbonic acid will convert to carbon dioxide and water.\u00a0 If the blood becomes too basic, carbonic acid will convert to bicarbonate and H+ ions:\r\n

\u00a0CO2<\/sub> + H2<\/sub>O \u2194 H2<\/sub>CO3<\/sub> \u2194 HCO3<\/sub>-<\/sup> + H+<\/sup><\/strong><\/p>\r\n\r\n

Acids, Bases, and\u00a0Enzymes<\/h1>\r\n<\/div>\r\nMany acids and bases in living things provide the pH that\u00a0[pb_glossary id=\"5757\"]enzymes[\/pb_glossary]\u00a0need. Enzymes are biological catalysts that must work effectively for\u00a0[pb_glossary id=\"5673\"]biochemical reactions[\/pb_glossary]\u00a0to occur.\u00a0Most enzymes can do their job only at a certain level of acidity.\u00a0[pb_glossary id=\"5665\"]Cells[\/pb_glossary]\u00a0secrete [pb_glossary id=\"1183\"]acids[\/pb_glossary] and [pb_glossary id=\"5715\"]bases<\/span>[\/pb_glossary]<\/span>\u00a0to maintain the proper pH for enzymes to do their work.<\/span>\r\n\r\nEvery time you digest food, acids and bases are at work in your\u00a0digestive system. Consider the\u00a0enzyme\u00a0pepsin, which helps break down\u00a0[pb_glossary id=\"5813\"]proteins\u00a0[\/pb_glossary]in the stomach. Pepsin needs an [pb_glossary id=\"5691\"]acidic[\/pb_glossary] environment to do its job. The stomach secretes\u00a0a\u00a0strong [pb_glossary id=\"1183\"]acid[\/pb_glossary] called hydrochloric acid that allows pepsin to work. When stomach contents enter the\u00a0small intestine, the acid must be neutralized, because enzymes in the small intestine need a basic environment in order to work. An organ called the\u00a0pancreas\u00a0secretes a\u00a0[pb_glossary id=\"5715\"]base[\/pb_glossary]\u00a0named bicarbonate into the small intestine, and this base neutralizes the acid.\r\n
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Feature: My\u00a0Human Body<\/h1>\r\n<\/div>\r\nDo you ever have heartburn? The answer is probably \"yes.\" More than 60 million Americans have heartburn at least once a month, and more than 15 million suffer from it on a daily basis. Knowing more about heartburn may help you prevent it or know when it's time to seek medical treatment.\r\n\r\n[caption id=\"attachment_1355\" align=\"alignright\" width=\"303\"]\"Image Figure 3.12.4. Acid reflux results when the esophageal sphincter doesn't close completely.<\/em>[\/caption]\r\n\r\nHeartburn doesn't have anything to do with the\u00a0heart, but it does cause a burning sensation in the vicinity of the chest.\u00a0Normally, the acid secreted into the stomach remains in the stomach where it is needed to allow pepsin to do its job of digesting\u00a0proteins. A long tube called the esophagus carries food from the mouth to the stomach. A sphincter, or valve, between the esophagus and stomach opens to allow swallowed food to enter the stomach and then closes to prevent stomach contents from backflowing into the esophagus. If this sphincter is weak or relaxes inappropriately, stomach contents flow into the esophagus. Because stomach contents are usually acidic, this causes the burning sensation known as heartburn. People who are prone to heartburn and suffer from it often may be diagnosed with GERD, which stands for gastroesophageal reflux disease.\r\n\r\nGERD\u00a0\u2014 as well as occasional heartburn\u00a0\u2014\u00a0often can be improved by dietary and other lifestyle changes that decrease the amount and acidity of reflux from the stomach into the esophagus.\r\n