The Science of pH and Why it Matters

Monica Macaes
5 days ago
3 min read

The term pH stands for potential of hydrogen, referring to a logarithm scale that indicates if a certain concentration of a solution is acidic or basic. This article will uncover the nuances behind the science and applications of pH.

Image 1 (pH logarithm scale)

It is crucial to analyse the pH in controlled environments. During an experiment, a mean that is not neutral (pH of 7), could interfere in the results. That is true since hydrogen ions (H+) act as a catalyst (compound that accelerates reactions), making it easier to break bonds and increasing the overall reaction velocity, which liberates H3O+ (H+).

Still, acid and base salts can interact, depending if the salts contain ions of strong acids or strong bases - salt hydrolysis. In this sense, strong acids do not interact with strong acids, and weak acids do not interact with weak acids, whereas strong acids dominate weak ones. (HO, 1975)

Image 2 (ion acid-base classes)

By combining an acid (compound with a pH lower than 7) and a base (compound higher than 7 - usually characterized by the hydroxyl OH-), there is a neutralization reaction, in which one obtains water and a determined kind of salt. Also, acids ionize, while bases dissociate their ions. However, it is not true to specific situations, especially concerning Brønsted-Lowry acids - the definition of acids and bases through proton transfer. Neither is it true for Lewis acids, defined in 1923, which gain a pair of electrons from bases, both conducting electricity in water.

Image 3 (example of electrolyte acid solution of citric acid)

Also, pH is crucial in biology, since it optimizes cellular enzyme action through metabolism maintenance. Furthermore, it interferes in the digestive system, cellular activity, solubility of nutrients (the more acid the more soluble), and activation of pH-sensitive molecules in the cell membrane. (EMOTO, 1995).

Highlighting climate issues, the acidic character of CO2 inhibits ocean acidification and coral death, as well as the vital effect on water quality, acidic rain, soil quality, agricultural productivity and ecosystem balance. (FLYNN, 2012).

Image 4 (ocean acidification and coral descarbonatization)

The process of detecting pH usually involves I) bromothymol blue (BTB) , or II) phenolphthalein indicators.

I) Image 5

II) Image 6

One can use pH to examine the concentration of an unknown liquid through titration, a chemical analysis that involves precise measurement of the volume needed to achieve neutralization (ONUFRIEV, 2001).

Image 7 (diagram of a traditional titration)

Reference List

FLYNN, Kevin J. et al. Changes in pH at the exterior surface of plankton with ocean acidification. Nature climate change, v. 2, n. 7, p. 510-513, 2012.

EMOTO, Noriaki; YANAGISAWA, Masashi. Endothelin-converting enzyme-2 is a membrane-bound, phosphoramidon-sensitive metalloprotease with acidic pH optimum. Journal of Biological Chemistry, v. 270, n. 25, p. 15262-15268, 1995.

ONUFRIEV, Alexey; CASE, David A.; ULLMANN, G. Matthias. A novel view of pH titration in biomolecules. Biochemistry, v. 40, n. 12, p. 3413-3419, 2001.

HO, Tse-Lok. Hard soft acids bases (HSAB) principle and organic chemistry. Chemical Reviews, v. 75, n. 1, p. 1-20, 1975.

WOOLERY, G. L. et al. On the nature of framework Brønsted and Lewis acid sites in ZSM-5. Zeolites, v. 19, n. 4, p. 288-296, 1997.

The Science of pH and Why it Matters

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