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|Chapter Two: The Chemistry of Biology|
Acids and bases are a way of classifying compounds based upon what happens to them when you place them in water.
Acids are substances that, when dissolved in water, split into two ions, one of which is an H+ ion (The H indicates that the ion is hydrogen, and the + indicates that it is positively charged, meaning that there is no electron.). A well known acid is HCl (hydrochloric acid), which splits into two ions when placed in water: H+ and Cl-.
When a base is dissolved in water, it splits into ions as well. For a base, one of them is OH- (often called a hydroxide ion). For example, NaOH splits into Na+ and OH- when placed in water, so it is a base.
If you put both an acid and a base into the same container of water, they tend to cancel out the effects of one another. For example, if both HCl and NaOH are placed in water, the Na+ and Cl- ions combine to form NaCl (table salt), and the H+ and OH- ions combine to form H2O (water).
Acids that release more H+ ions than other are said to be more acidic, and bases which release greater amounts of OH- ions are more basic. The extent to which a compound is acidic or basic is measured by the pH scale. On the scale, numbers range from 0 (most acidic) to 14 (most basic). Water has a pH of 7, which is neutral.
Buffers are compounds that tend to neutralize the pH of a solution by combining with either H+ ions or OH- ions to keep the solution neutral. Buffers play a very important role in most organisms, as many organisms cannot live at pHs that are too acidic or too basic. This is because certain reactions which occur in organisms are hindered by the effects of an excess of charged ions in the environment (The reasons for this will become clearer when enzymes are discussed later in this chapter.).