What is PH

pH is a measure of acidity or alkalinity which indicates the amount of hydrogen ions present in a solution or substance.

The acronym pH means potential hydrogen or potential of hydrogen ions, from the Latin pondus: weight, power: power e hydrogenium: hydrogen, that is pondus hydrogenii either potentia hydrogenii.

The terminus was designated by the Danish chemist Sørense when he defined it as the opposite of the base 10 logarithm or the negative logarithm of the activity of hydrogen ions, whose equation is pH= -log10[aH+].

Summary of Contents

pH scale


pH can be measured in an aqueous solution using a numerical value scale that measures acidic (higher concentration of hydrogen ions) and alkaline (base, lower concentration) solutions of substances.

The numerical scale that measures the pH of substances includes numbers from 0 to 14. The most acidic substances are close to number 0, and the most alkaline (or basic) are those that are close to number 14. However, there are neutral substances such as water or blood, whose pH is between 7 and 7.3.

Acid substances such as lemon juice have a pH between 2 and 3 or urine between 4 and 7. For its part, gastric juices have a value between 1 and 2 or battery acids that are between 1 and 0.

On the contrary, alkaline or base substances have higher values ​​such as milk of magnesia between 10 and 11 or cleaners with ammonia whose value is between 11 and 12.

You can also calculate pH measurements using a potentiometer or pH Meter, which is a sensor that determines the pH of a substance through a glass membrane that separates two solutions of different concentrations of protons.

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Another way to find out approximately the acidity of a substance is by using an indicator paper known as litmus paper, which has components that indicate the pH of a substance based on the change in color that the paper undergoes.

See also:

  • Ionization.
  • Base.

soil pH

It is a measure of soil acidity or alkalinity and is considered an important soil variable as it affects mineral uptake by plants. That is, it harms the development of plants and the biological activity of the soil.

The recommended levels of soil pH have a measurement between 5.5 and 7. However, there are plants that grow and develop in extreme environments where the levels of acidity or alkalinity of the soil are highly variable. On the other hand, the pH measurements that are used to carry out the agriculture of certain foods can vary.


The pOH is the negative logarithm to the base of 10 of the activity of the hydroxyl anions. It has the same properties as the pH in an aqueous solution with a value between 0 and 14, but in this case solutions with pOH greater than 7 are acidic, and those with values ​​less than 7 are basic or alkaline.

It is represented by the equation pOH = – log[OH].

buffer solutions

Buffer, regulatory or buffer solutions are used to maintain the level of acidity or alkalinity of a substance during a chemical reaction in a short period, this in order to prevent other unwanted chemical reactions from occurring.

See also: Acids and bases and chemical change.

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