Bio 100 reading on pH Instructor Deborah Bird Page | 1 Introduction to pH As you learned in the previous assignment an ion is an atom that has lost or gained electrons, and has become electrically charged (+ or -). Ions behave differently than uncharged atoms because of this charge. Ions are very important in our life processes -- in fact we'd die without them. Of all the ions in your body, none is more important than the hydrogen ion (H+). Hydrogen ion is formed when a hydrogen atom loses its electron. In effect, a hydrogen ion is the same thing as a proton. The hydrogen atom has no neutrons, so when it loses its electron al that is left is a proton. The term pH refers to the concentration of hydrogen ions (H+) in water. Biologists are interested in H+ concentration because it has such a great effect on chemical reactions. Behavior of singled cell organisms, as well as, multicellular organisms is linked to pH levels in and outside of the cell. pH affects the the structures and activities of biological molecules. This is why we monitor the pH in fish aquaria and in swimming pools to avoid potential problems. In the case of the aquarium, we're trying to maintain a life-sustaining environment for microorganisms; in the swimming pool, we're trying to prevent microbes from growing. A small change in concentration of H+ can have a dramatic effect. The blood of humans is so sensitive to H+ concentration that a pH change from 7.4 to 7.2 or 7.6 can result in death. Imagine a water molecule. If the molecule breaks apart, the electron from one of the hydrogen atoms leaves the hydrogen completely, and instead stays with the oxygen-hydrogen complex that formed the remainder of the water molecule. We now have a hydrogen ion (the hydrogen that lost its electron, i.e. H+) and a hydroxyl ion (i.e., OH-).Bio 100 reading on pH Instructor Deborah Bird Page | 2 If we put these two ions back together, we have a water molecule again. In a glass of water, some of the molecules will spontaneously break apart while others are joining back together. If we count the number of hydrogen ions and hydroxyl ions in the glass of water, they will be equal (since one of each is produced when a water molecule breaks apart). When the number of hydrogen ions equals the number of hydroxyl ions, we say a solution is pH neutral. A neutral solution has a pH value of 7. A solution with more hydrogen ions than hydroxyl ions is an acid. All compounds having a number below 7 on the above chart are considered to be an acid. Notice this also includes pure rain water. The smaller the pH number the more acidic the solution. acid baseBio 100 reading on pH Instructor Deborah Bird Page | 3Each number represents 10 times more H ions as the numbers become smaller. In other words, a pH of 5 has ten times more H ions than a pH of 6. Notice that gastric fluid is almost a pH of 1. The acidic contents of the stomach help with the digestion process. An acid is also a substance that releases or causes the release of H+ into solution. Some common acids are hydrochloric acid, acetic acid, carbonic acid, and sulfuric acid. All of these contain hydrogen. When dissolved in water, they release hydrogen ions, and the pH of the solution is low (acidic). A compound does not have to contain hydrogen itself in order to be an acid. Carbon dioxide (CO2), for example, can combine with water to generate H+. The reaction of SO2 (sulfur dioxide) is similar to that of CO2. The presence of SO2 in the atmosphere is partially responsible for acid rain. In May 2008 th science daily reported that “ an international team of scientists surveying the waters of the continental shelf off the West Coast of North America has discovered for the first time high levels of acidified ocean water within 20 miles of the shoreline, raising concern for marine ecosystems from Canada to Mexico”. Chemistry matters. A base is a substance that can remove H+ from solution, lowering the concentration of H+. Many bases ionize to produce hydroxyl ions (OH-) which combine with H+ to make water (H2O). Some common bases are sodium hydroxide (NaOH), magnesium hydroxide (Mg(OH)2), and potassium hydroxide (KOH). Bases have pH values greater than 7. We can tell how strong an acid or base is by looking at the pH value. A very low number (2 for example) indicates a strong acid (the minimum is 0). A substance of pH 6 would be a weak acid (closer to 7). A pH value of 12 would indicate a strong base (the maximum is 14). A pH of 8 would indicate a weak base. Each step on the pH scale (4 to 5 or 6 to 7) actually means a ten-fold difference in concentration of hydrogen ions. Each step UP on the pH scale means that there are 10x more OH- ions and 10x fewer H+ ions than the step below. Each step DOWN the pH scale means there are 10x more H+ and 10x fewer OH- than the step above. For example, a solution with a pH value of 6 has 10x more hydrogen ions than a solution with a pH value of 7. A buffer is a chemical that minimizes changes in pH. Buffers can remove hydrogen ions or add hydrogen ions to a solution, without themselves being changed in a major way. In some areas of the country, water has chemicals in it that act as buffers. InBio 100 reading on pH Instructor Deborah Bird Page | 4these areas, lakes and streams are usually seriously affected by acid rain, since the buffers minimize changes in pH. However, if enough acid is added to the lake, the buffers can’t keep up, and eventually pH