What is ionization? definition and meaning - With a predictable frequency, water itself can ionize into a hydrogen ion (H+) and hydroxide ion (OH-),thus providing the ions required in many fundamental reactions essential to the continuation of life. In addition, other molecules containing H+ and OH- groups dissociate in water. A substance that releases hydrogen ions (H+) is called an acid. Substances that release hydroxide ions (OH-) in water are called bases. (This is not a complete definition of an acid or base, but it will serve our purposes.)
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We use a scale called pH, which runs from 0 to 14, to indicate the relationship between these two ions in solutions. In pure water, the numbers of hydrogen ions (H+) and hydroxide ions (OH-) are equal; hence the water is said to have a neutral pH, or a pH of 7. When the number of H+ exceeds the number of OH-, the solution is said to be acidic, and has a pH of less than 7. Conversely, when the number of OH- exceeds the number of H+, the solution is said to be basic or alkaline; it has a pH between 7 and 14 (Figure 2.15). The scale is based on powers of 10, so that the difference of just one indicates a change ten times as great. For example, stomach acid has an acidity level around 2. Apples have a pH of about 5. That means that stomach acid is 1000 times as acidic as apples.
Chemical reactions of living organisms usually occur at a pH range of 6.9 to 7.5, a range that is called "neutral." (There are exceptions, such as the highly acidic environment inside your stomach.) However, many of the chemical reactions that occur in aqueous solutions either release or utilize hydrogen, which affects the pH. How does the cell prevent pH shifts away from neutrality? The maintenance of the internal pH of all cells is primarily due to buffers, chemical substances that play one of two roles. When there are too many hydrogen ions (when the solution is acidic), buffers combine with excess hydrogen ions to bring the solution to a neutral state. When there are too many hydroxide ions (when the solution is basic), buffers combine with hydroxide ions to bring the solution to a neutral state. Hence neutrality is maintained.
Carbonic acid is one of the major buffering substances of blood. Carbonic acid when present in water dissociates into bicarbonate and hydrogen ions. When chemical reactions in the body cause a high concentration of hydrogen ions in the blood, they combine with the bicarbonate to form carbonic acid, thus removing the hydrogen ions from the blood. When there is an excess of hydroxide ions, they combine with the hydrogen ions to form water. (Source: Avila, Vernon L. Biology : Investigating Life On Earth Jones and Bartlett/Bookmark Series in Biology Page 46-48)
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