Tuesday, May 27, 2008

We don't realize how unique water is. For instance, it is one of the very few substances which floats on freezing. The structure of water molecules make this possible. There are weak interactions between individual water molecules which give water it's surface tension. Surface tension makes it possible for bugs to walk on water. The crystalline structure of ice is actually less dense than water so ice floats. What would happen to the fish if our lakes froze from the bottom up? Water, H₂O, dissociates into H⁺ and OH^-. The concentration of these ions determine pH. Water has a pH of 7 which is considered neutral. The separate ions are present at a concentrations of 2x10^-7 or 0.0000001. When an acid such as vinegar is added to water it increases the H⁺ to a concentration to say 1x10^-3 or 0.001 which would be a pH of 3. When a base such as ammonia is added to water it increases the OH^- concentration and decreases the H⁺ concentration to perhaps 1x10^-10 or pH of 10. pH meters, along with appropriate pH electrodes are used to determine pH in the laboratory. A pH determination must always be made against a standard pH buffer. There are also portable pH meters for pH determinations in the field. An estimate can be made of pH by using pH paper or pH strips. The paper contains a chemical which turns red at low pH and blue at high pH. A neutral pH would have no change in color. One would compare the color of the paper to a chart for an estimate of the pH. A buffer is a chemical which when added to a solution resists changes in pH when an acid or base is added. No aqueous chemical process can proceed without attention to pH. Robin Prymula