pH, an acronym for Potential of Hydrogen (i.e., the presence of positive ions or cations), is the index that indicates the acidity, alkalinity or neutrality of any liquid solution in which the solvent is water, which is the same as saying “aqueous”. The scale that measures it varies between 0 and 14, with the neutral point being 7. If the pH value is equal to 7, the solution is neutral; if less than 7, it is acidic; if it is greater than this value, it is base or alkaline.


However, simply increasing or decreasing one unit on the scale does not mean that the solution is only one time more alkaline or acidic. pH is measured according to a logarithmic scale, i.e. a decrease or increase of one unit is always multiplied by ten for each unit. For example, a pH of 5 is ten times more acidic than a pH of 6, and a hundred times more acidic than a pH of 7.


As for measurement methods, although in an industrial context it is common to use highly sophisticated devices that provide electronic readings, the most common way is the use of acid-base indicators, i.e., substances that change colour to indicate the result.


Among the most commonly used is phenolphthalein, which becomes colourless when added to an acidic medium and pink in an alkaline medium. All one has to do is to compare the shade with a scale with different colours to obtain the result; another is litmus paper (a mixture of different organic pigments extracted from lichens), which turns red in the presence of acids and blue in the presence of bases.


Obtaining pH values is also possible from natural elements. The spontaneous emergence of plant species in the soil is a good indicator of its acidity or alkalinity, as these species only develop under certain conditions. Another good example provided by botany is that of the hydrangea, which, when it has a blue flower, indicates an acidic soil, and when pink, an alkaline soil.

The pH scale was created in the second half of the nineteenth century, when the study of chemistry was flourishing and many physicochemical concepts were established.


As is the case with many scientific discoveries, what seemed obvious was not found to be true, and it was not because of water, in its pure state, that the first need to measure pH arose.


The father of the discovery was the Danish biochemist Soren Sorensen, then director of the laboratory of a beer brand in that Scandinavian country. Concluding that it would be important to control the amount of hydrogen ions in the beer, as this would have an effect on the final product, he created the pH notation and the corresponding scale. The “p” comes from the German “potenz” or the French “puissance” (there is no consensus among the scientific community as to its origin), while the “H” stands for hydrogen ions (H+). 

If health, the widest range of organisms or vastly different human activities all depend on the constancy of pH, it also proves to be a determining factor for the planet Earth as a whole. Due to the close relationship between the various ecosystems, a significant deviation in the pH balance in one of the “pillars” of the planet can trigger a chain reaction and, ultimately, determine the existence of Life itself.


This is the case with respect to the oceans, where changes in pH are highly significant indicators of the impact of climate change. According to data published by the United States Environmental Protection Agency (EPA), levels of carbon dioxide in the atmosphere increased by about 40% from pre-industrial levels to the beginning of the twenty-first century, i.e. by ten times more than over millions of years on Earth. When CO2 dissolves in water, it causes several chemical reactions that result in higher acidity. The effect is further driven by the precipitation of so-called “acid rains”, the pH of which is typically between 4.2 and 4.4.


As a result - reveals the above North American agency - before the Industrial Revolution, the average pH of the oceans was around 8.2, but today it is around 8.1. It may not seem significant, but in reality, due to the logarithmic scale of measurement, it means that the acidity of the ocean is today, on average, about 25% higher than it was in pre-industrial times. This is an increase never before seen since the recording of the geological past of the planet began, and reflects that the acidity of the oceans is greater than at any time in the last two million years.


But the tendency is for this change to become more drastic. Also according to the EPA, the decrease could reach up to 0.4 units near the end of the century, which would represent a 120% increase in the acidity of the water. This fact would have an unprecedented impact on marine ecosystems and on the billions of people who depend on the ocean for their survival.


The apparent simplicity of the scale created by Sorensen reveals the beauty of balance, but it can also reflect overwhelming realities. Because moving from red to blue may actually make a huge difference.