Increasingly basic

Neutral—neither acidic nor basic

Increasingly acidic i

Increasingly acidic i

Acid and Base Concentrations

Concentrations of acids and bases affect the chemical reactions that constitute many life processes, such as those controlling breathing rate. Thus, the concentrations of these substances in body fluids are of special importance.

Hydrogen ion concentration can be measured in grams of ions per liter of solution. However, because hydrogen ion concentration can cover such a wide range (gastric juice has 0.01 grams H+/liter; household ammonia has 0.00000000001 grams H+/liter), a shorthand system called the pH scale has been developed. This system tracks the number of decimal places in a hydrogen ion concentration without having to write them out. For example, a solution with a hydrogen ion concentration of 0.1 grams per liter has a pH value of 1.0; a concentration of 0.01 g H+/L has pH 2.0; 0.001 g H+/L has pH 3.0; and so forth. Between each whole number on the pH scale, which extends from pH 0 to pH 14.0, there is a tenfold difference in hydrogen ion concentration. Note that as hydrogen ion concentration increases, pH value decreases.

In pure water, which ionizes only slightly, the hydrogen ion concentration is 0.0000001 g/L, and the pH is 7.0. Because water ionizes to release equal numbers of acidic hydrogen ions and basic hydroxyl ions, it is neutral.

The concentrations of hydrogen ions and hydroxyl ions are always in balance, such that if one increases, the other decreases, and vice versa. Solutions with more hydrogen ions than hydroxyl ions are acidic. That is, acidic solutions have pH values less than 7.0 (fig. 2.9). Solutions with fewer hydrogen ions than hydroxyl ions are basic (alkaline); that is, they have pH values greater than 7.0.

Table 2.5 summarizes the relationship between hydrogen ion concentration and pH. Chapter 21 (pp. 868-871) discusses the regulation of hydrogen ion concentrations in the internal environment.

Many fluids in the human body function within a narrow pH range. Illness results when pH changes. The normal pH of blood, for example, is 7.35 to 7.45. Blood pH of 7.5 to 7.8, called alkalosis, makes one feel agitated and dizzy. This can be caused by breathing rapidly at high altitudes, taking too many antacids, high fever, anxiety, or mild to moderate vomiting that rids the body of stomach acid. Acidosis, in which blood pH falls to 7.0 to 7.3, makes one feel disoriented and fatigued, and breathing may become difficult. This condition can result from severe vomiting that empties the alkaline small intestinal contents, diabetes, brain damage, impaired breathing, and lung and kidney disease.

What is a molecular formula? A structural formula? Describe three kinds of chemical reactions.

Compare the characteristics of an acid with those of a base.

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Essentials of Human Physiology

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