The pH of a solution describes the level of its alkalinity or acidity. The pH scale is 0 to 14, with 7 being neutral. Below 7 indicates acidic, and numbers higher than 7 mean it is alkaline. The pH may be tested by using litmus paper that changes color when it is dipped into a solution. The color is compared to a chart that shows the estimated pH level. For more accurate measurements, a pH meter is used.
Description
A pH meter is an electronic device that includes the meter itself, a reference electrode and an electrode that measures pH, according to Omega Engineering. The pH measurement electrode generates voltage that is proportional to pH. Copidate Technical Publicity indicates that the reference electrode is used to complete the electrical circuit with a connection of zero voltage. There are many types of pH meters, from portable to bench-top units.
Uses
There are numerous types of applications for a pH meter. The U.S. Geological Survey (USGS) measures the pH of water samples in the hundreds of thousands each year to test the quality of the water. A pH meter is used extensively in the medical field for the testing of bodily fluids, as well as in industry and manufacturing, such as in making beer and wine, testing cosmetics and checking the quality of foods. Determining the pH of soil is also necessary for plant health, according to ph-meter.info. (Soil is mixed into distilled water for testing.)
Operation
The measurement electrode is placed in the solution to be tested. The reference electrode is placed in a buffer solution that is a fixed pH level. USGS indicates that the pH meter measures the difference of voltage between the two electrodes. The difference is translated by the meter and displayed as pH on the screen.
Calibration
Before using a pH meter, it must calibrated. To calibrate it, solutions of known values are used to adjust the settings on the meter. For example, Dartmouth College indicates that a buffer solution of 4 should be used to set the first knob (Cal 1) and a buffer solution of 10 for adjustment of the second knob (Cal 2). Between solutions, the electrode should be rinsed and blotted dry. After completing the calibration, each solution should be tested again to determine that the meter is giving consistent readings.
Considerations
Cornell University suggests that pH meters should be purchased through a scientific supply company, such as Hanna Instruments or Cole-Parmer Instrument Company. Costs range from under $100 to more than $1000 (as of 2010). Temperature can affect pH readings. Purchasing a meter that compensates for temperature automatically may be beneficial. Copidate Technical Publicity indicates that depending on the type and extent of their use, electrodes wear out over time and need to be replaced.
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