PH: The beauty of balance

In the complex and comprehensive world of chemistry, there are few measurement units that are as cross-cutting as pH. The simple scale that measures it can reveal well-kept secrets or give an indication that it is necessary to react to a potential problem. Because there is much more than what the small strip that goes from red to blue tells us.


The measurement

The pH, acronym for Hydrogen Potential (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 it is lower than 7, it is acidic; if it is higher than this value, it is basic or alkaline.

However, simply increasing or decreasing one unit on the scale does not mean that the solution is just once more alkaline or acidic. The pH is measured according to a logarithmic scale, that is, the 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 highly sophisticated devices that provide electronic readings are frequently used in an industrial context, the most common form is the use of acid-base indicators, that is, substances that change color to indicate the result.

Among the most used is phenolphthalein, which is colorless when added to an acidic medium and pink in an alkaline medium, and then it is enough to compare the shade with a scale with different colors to obtain the result; another is litmus paper (a mixture of various 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 appearance of plant species in the soil is a good indicator of its acidity or alkalinity, as these same species only develop under certain conditions. Another good example that botany brings us is that of hydrangea, which when it has a blue flower indicates acidic soil, and when pink it indicates alkaline soil.

Water? No. beer

The creation of the pH scale occurred in the second half of the 19th century, a time when the study of chemistry was flourishing and many physico-chemical concepts were established.

As in many scientific discoveries, even in this case what seemed obvious was not verified, and it was not through water, in its pure state, that the first need to measure pH appeared.

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 relevant to control the amount of hydrogen ions in beer, since this would have effects on the final product, he created the pH notation and the corresponding scale. The “p” originates from the German “potenz” or the French “puissance” (the origin is not consensual among the scientific community), while the “H” stands for hydrogen ions (H+).

From agriculture to the human body

The knowledge of pH values is an important ally in various sectors of activity, such as agriculture, agronomy, aquaculture, biology, engineering (food, environmental, civil, forestry, chemistry, materials), medicine, and others.

In agriculture, soil acidity or alkalinity is a determining factor for crop success, as each species requires an adequate pH for its development. For example, corn requires a pH of 5.5 to 7.5, while rice performs better in soils with a pH between 5.0 and 6.5. Knowing the acidity level of the soil and the needs of different crops, it is possible to correct the pH by adding chemical substances.

Other areas where maintaining an adequate pH level is crucial is human blood. Its permanence within a certain range (between 6.9 and 7.8) is essential for cell health. If these values are exceeded (more or less), you may have serious health problems or even be at risk of death.

The blood pH is considered to be slightly alkaline, as its normal index is between 7.35 and 7.45. Its entry at a lower level causes what is called acidosis, while a higher level of alkalinity indicates alkalosis.

A beacon for the planet

Whether health, the most diverse organisms or the most diverse human activities depend on the consistency of the pH, this also proves to be a determining factor for 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 planet's “pillars” can generate a chain reaction and, ultimately, determine the existence of Life.

This is the case of the oceans, whose observed changes in pH constitute a very relevant indicator of the impact of climate change. According to data published by the United States Environmental Protection Agency (EPA), carbon dioxide in the atmosphere increased by about 40% between pre-industrial levels and the beginning of the 21st century, ten times more than what occurred on Earth in millions of years. When CO2 dissolves in water, it causes several chemical reactions that result in higher acidity. The effect is further enhanced by the precipitation of so-called “acid rain”, whose pH is typically between 4.2 and 4.4.

As a result - reveals that North American body - before the Industrial Revolution, the average pH of the oceans was about 8.2, but it is currently about 8.1. It may not seem significant, but in reality, due to the logarithmic measurement scale, 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 observed before since there are records of the planet's geological past, which reveals that the acidity of the oceans is greater than at any other time in the last two million years.

But this change tends to increase. Also according to the EPA, the decrease could reach up to 0.4 units near the end of the century, which would represent water up to 120% more acidic. This 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 from red to blue there can indeed be a big difference.

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