pH – Chemistry – Natural Sciences
We explain what pH is and what instruments are used to measure it. The pH scale and examples of acidic, neutral, and base compounds.
What is pH?
pH is a measure used to establish a solution’s acidity or alkalinity level. The “p” stands for “potential,” which is why pH is called: the potential of hydrogen.
It is expressed as the base ten negative logarithms of the hydrogen ion concentration. The following equation represents this definition:
pH
Equation 1: Equations to calculate pH and POH.
On the other hand, pOH measures the concentration of hydroxyl ions in a solution. It is expressed as the base ten negative logarithms of the hydroxyl ion concentration and, unlike pH, is used to measure the alkalinity level of a solution.
An additional fact is that in an aqueous solution at 25 ºC, the pH and pOH sum equals 14.
What is the relationship between acidity level and pH?
Acid solutions have a high amount of hydrogen ions. This means that they have low pH values (see equation 1), and their acidity level is high. Thus, a solution will be more acidic or less acidic depending on the number of hydrogen ions it has.
On the other hand, essential (alkaline) solutions have low amounts of hydrogen ions. This means that they have high pH values (see equation 1), and their acidity level is low.
The pH measurement scale
The pH scale measures the degree of acidity of a solution. Since the pH is related to the pOH (see equation 1), then knowing the degree of sharpness of a solution, we can also understand its degree of basicity.
Thus, the pH scale goes from 0 to 14. For example, substances with a pH value=0 are the most acidic (less basic), those with pH=7 are neutral, and those with pH= 14 are the least acidic (most basic).
Examples of Acidic, Basic, and Neutral Compounds
Examples of Acidic Compounds
Battery acids. They have pH values between 0 and 1. Their acid level is so strong that it is detrimental to the species.
Acid rain. It is a phenomenon produced by the accumulation of acids from fossil fuels. These rains can take pH values between 2 and 5 on the pH scale. When the pH approaches 2, it can cause the death of fish, plants, and other species. When the pH is close to 5, it produces less damage but still affects aquatic and terrestrial life.
Lemon juice. It has pH values between 2 and 3.
Coffee. It has a pH value=5 or very close values.
Examples of neutral compounds
- Blood
- Milk
Examples of basic compounds
Milk of magnesia. The pH table is located between the values 10 and 11. This product is for consumption
Bleach or chlorine. It has pH values around 13. It is used for cleaning the home, bathrooms, and kitchen and has the power to discolor clothes.
How is pH measured?
The way to distinguish between an acidic and a primary compound is by measuring its pH value. Currently, there are numerous methods to measure the pH of a substance.
Using acid-base indicators. Indicators are compounds that change color by changing the pH of the solution in which they are found. For example, phenolphthalein is a liquid that turns pink when added to a base and colorless when added to an acid. Another example is litmus paper: if a fragment is immersed in an acidic solution, it turns red-orange, and if it is engaged in a basic solution, it darkens to a blue color. Some types of litmus paper with more specific color scales indicate more accurate pH values.
Using a potentiometer or pH meter. It is electronic equipment that directly gives us the pH value of a solution. The pH measurement utilizing this equipment is more accurate than using litmus paper.
What are buffer solutions or buffers?
Buffer solutions or Buffers keep the pH of a solution constant, even when specific amounts of acid or base are added.
Buffer solutions are vital in regulating the pH of many biological processes because, for many of them t,o be the pH of the medium in which they occur must remain constant.
