What is pH and Why is It Important?
pH, Hydrogen Ion Concentration is Significant in Chemistry and Life
Often pH is measured for soil, water, blood, urine and related clinical specimens, and many chemical reactions; pH is an important value that has significance and consequences. Even spas and swimming pools require pH checks, otherwise disinfectants may not be active.
Basic Concepts of pH are Related to Water Ionization
The pH is a measure of hydrogen ion concentration. A sample of absolutely pure water has a pH value of 7.0. The pH scale ranges from 0 (acid) to 14 (basic). A pH of 7.0 is considered neutral pH.
Pure water ionizes to a limited degree to form H + (protons) and (OH) - hydroxyl ions: HOH (water molecule) —> H+ and (OH)-. Notice that one molecule of water can ionize into one hydrogen ion and one hydroxyl ion. For pure water exactly equal amounts of protons and hydroxyl ions are produced. The ionization of pure water molecules is rare — only 1 in every 10 million water molecules (1/10,000,000) dissociates.
pH Defined and Ways to Measure pH
Scientists determined a simple, convenient, numeric way to express pH as the logarithm (to the base 10) of the reciprocal (inverted number) of the hydrogen ion concentration. Thus, 1 in 10 million reciprocated is 10 million, and the log 10 value of that is 7.0.
Whenever pH is measured, hydrogen ion concentration is determined. Thus, pH values of 5.0, 3.0 and 1.0 express, respectively, that 1 in 100,000, 1 in 1,000 and 1 in 10 concentrations of hydrogen ions (protons) are present. These acidities occur in weaker, organic acids (citric, acetic and lactic acids) and strong, inorganic acids (HCl, hydrochloric acid; HNO3, nitric acid; H2SO4, sulfuric acid). When strong bases are measured, as in NaOH (sodium hydroxide) and KOH (potassium hydroxide), the pH values approach 13 and 14 with decreased and rare H+, and much increased (OH)-. Inorganic acids and bases are joined by ionic bonds and ionize readily.
Measurement of pH can be done simply with:
- select color indicators (incorporated into pH paper, or solutions) such as methyl violet, congo red, methyl red, phenol red, litmus and phenolphthalein can detect defined pH ranges.
- pH meters that detect hydrogen ion concentrations.
Importance of pH in Living Systems, Chemistry and Biochemistry
Photos below this article show several typical pH values. The second photo clearly indicates the hydrogen ion concentration and pH relationship. Note that battery acid, acidic fruits and vegetables have low pH values; pure water is neutral pH 7.0, and bleach and drain cleaners are at the high end of pH with few H+ (protons) and many OH- (hydroxyl ions).
Why is pH significant? pH influences the structure and the function of many enzymes (protein catalysts) in living systems. Some enzymes have narrow ranges of pH activity. Pepsin, a stomach enzyme works best at pH 2. In the duodenum, trypsin functions optimally around pH 7.5–8.0. Overall, most human cell enzymes work best in a slightly alkaline environment of about 7.4.
Cellular pH is so important that death may ensue within hours if a person becomes acidotic. One such example is unregulated diabetes — high blood sugar occurs and acids form that rapidly destroy enzymes and cells. Regular blood sugar monitoring always is important for diabetics.
In other cases, alkalosis may occur with pH values of 7.6–7.8 or greater, with equally damaging consequences. Typically, natural buffers in the body such as NaHCO3 and proteins regularly compensate for some smaller, acidic and alkaline pH shifts.
In summary, pH which is a measure of hydrogen ion concentration, is critical to life and biochemistry and many important chemical reactions.
Resources
Alters, S and B. Alters. 2006, Biology. John Wiley & Sons Inc., Hoboken, N.J. 755 pp
pH Scale and Typical pH of Common Items
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pH Scale Hydrogen Ion Values and pH Common Substan
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pH Paper for 4.0-10.0 Measurements
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pH Paper Test for Water Evaluation
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pH Meter for 0-14 pH Solution Tests
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