06 Aug


pH meters, along with appropriate pH electrodes are used to determine pH.  pH is defined as the negative log of the Hydrogen ion concentration (not percent Hydrogen).  Water, H2O, dissociates into H+ and OH- ions. The concentration of H+ and OH- determines the pH of a solution. Water has a pH of 7 which is considered neutral. The separate ions H+ and OH- are present at a concentrations of 2×10-7 or 0.0000001. When an acid such as vinegar is added to water it increases the H+ to a concentration around 1×10-3 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 down to perhaps 1×10-10 or pH of 10.   A pH determination must always be made against a standard pH buffer.

There are portable pH meters for pH determinations in the field. An estimate can be made of pH by using pH paper or pH strips.  The technician dips the pH strip into the test solution and compares the color of pH strips 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. Hach, WTW, Thermo Orion, and Mettler Toledo are some of the manufacturers of pH meters.

Robin Prymula