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The pH scale indicates how strong an acid or alkaline solution is and is based on the concentration of hydrogen ions (H+ and OH-) in a solution. The pH measurement is important for water-quality standards and treatment. The pH scale is a number scale that runs from 0-14. The numbers 0-14 refer to the exponential value of the ion concentration. For example, the log of the concentration of hydrogen ions in water is 107 (when the sign of the exponent is changed, it becomes the number for the pH scale). The middle of the scale is 7, which indicates that the sample being measured is neutral and it's not an acid or base. Numbers below 7 indicate the sample is an acid with 0 being the strongest acid, and numbers above 7 indicate the sample is a base, with 14 being the strongest base. If process water from a factory is to be returned to a river, it must be neutral, so it will be tested to determine if it's acidic. If it's acidic, base material such as soda ash can be added to it to return it to a neutral substance. The table below has examples of common materials as they apply to the pH scale. A wide variety of sensors is available to measure pH in industrial applications. These sensors consist of a probe and a signal conditioner. The probe is placed in a location where it can sample the liquid being measured.
Table of pH Values
- 14-Lye 1 molar solution
- 13-dilute sodium hydroxide
- 12-lime water
- 11-household ammonia
- 10-milk of magnesia
- 9-baking soda
- 8-albumin
- 7-pure water
- 6-tap water (from a well)
- 5-black tea
- 4
- 3-vinegar
- 2-lemon juice
- 1
- 0-dilute sulfuric acid (battery acid)
Above: Table showing the pH value for some of the most common household products.
