Natural Sciences

PH scale

The pH scale is a mathematical representation that establishes the alkalinity level of a substance. The mathematical formula for this scale is the negative base 10 logarithm for hydrogen ions.

The scale determines which substances are acidic, alkaline, or neutral . To establish such characteristics, there is a 15-position line, more specifically, from 0 to 14.

Related Articles

What is pH and how is it measured

The pH is a measure of acidity or alkalinity pointing the amount of existing hydrogen ions in a substance. Some chemical reactions, in certain solutions, take place at a certain pH level, hence the importance of knowing where on the scale such a substance is at any given time.

The letters “pH” are the abbreviation of “pondus Hydrogenium”, or what is the same, hydrogen weight. His discovery arose with the study of water, when it was determined that the vital liquid is composed of ions and protons.

This factor is determined by the number of free hydrogen ions (H +) present in a substance.


The pH measurement can be done in two ways: through a pH indicator paper or through experimental laboratory processes. Both methods are based on the color change of the objects used for measurement.

To measure the pH of a substance, for example, water, the number of protons (H + ions) and the number of hydroxyl ions (OH-) must be considered. If that water sample contains the same number of ions and protons, then the water is neutral: its pH is approximately 7.

But, to know if the pH of a substance is adequate to carry out a certain process, its scale must be taken into account. Remember that the pH scale goes from 0 to 14; If the result of the measurement yielded a number greater than 7, it is said to be a basic substance. If it is less than 7 it is said to be acidic.

Being a base 10 logarithm, when a solution becomes ten times more acidic, the pH will decrease by one unit on the scale.

Types of substances according to their pH

  • Acids : has a value on the scale less than 7. These substances react with alkaline substances and have a sour or acid taste, like vinegar. Mixed with metals, they form salt and hydrogen, and contact with the skin can cause burns or irritation.
  • Alkaline : the result of its pH is greater than 7. They have a bitter taste and can also irritate the skin. They are excellent electrical conductors and react with acids. These substances are quite soluble. The ammonia is an example of such solutions.

Examples of pH scale

You will then see a list of substance with its pH value on the scale.

  • Hydrochloric acid (0)
  • Lemon juice (2.0)
  • Apples (3.0)
  • Wine (4.0)
  • Tomatoes (4.5)
  • Milk (6.6)
  • Pure water (7.0)
  • Human blood (7.4)
  • Baking powder (8.3)
  • Manganese (10.5)
  • Ammonia (11.0)
  • Lyme (12.4)
  • Bleach (13.0)
  • Sodium hydroxide (14.0)

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button