This page explains a concept from high-school chemistry regarding pH & H+ ion concentration of solutions. The pH value determines the acidity and alkalinity of a solution.
The pH value of a solution is related to the active positive Hydrogen ions (H+) concentration in the solution.
What is pH & H+ Ion Concentration
In chemistry, pH is used as a measure of the acidity or alkalinity of a substance. The pH scale runs from 0 to 14.
Substances with a pH less than 7 are considered acidic, and substances with a pH greater than 7 are said to be basic (alkaline).
Our bodies, for instance, must maintain a pH close to 7.35 in order for enzymes to work properly.
To determine whether a solution is acidic or basic (alkaline), we find its pH value, which is a measure of the number of active positive hydrogen ions (H+) in the solution.
The pH is defined by the following logarithmic function formula, where H+ is the active positive hydrogen ion concentration in the solution.
pH = -log(H+)
Conversely, the active positive hydrogen H+ ion concentration is related to the pH value by the inverse function (exponential) as below:
H+ = 10**(-pH)
Refer to the end of this page for more information on pH and H+ ion concentration.
The program below illustrates these relationship using NumPy and Python.
Molarity and pH
To get a feel for what is acidic and what is basic, the following are the pH levels of some common substances:
| Substance | pH | M (Molarity) mol/Liter |
|---|---|---|
| Battery acid | 0.8 | 5 |
| Stomach acid: | 2.7 | 0.1 |
| Pure water | 7 (at 25° C) | 55.56 |
| Human blood | 7.35 | |
| Fresh coconut: | 7.8 | |
| Sodium hydroxide | 14 | 17.6 |
For example, let us calculate the H+ ion concentration in battery acid, which has the pH value is 0.8. We will use the H+ ion concentration formula:
H+ = 10**(-pH)
Plugging in 0.8 as the pH value in the above formula, we get:
H+ = 10**(-0.8) = 0.148 Moles/Liter
This means that the H⁺ ion concentration in battery acid is approximately 0.158 moles per liter.
What is Molarity
The last column in the above table, we introduced a new name (molarity). Molarity is defined as the number of moles of solute per liter of solution.
- The uppercase “M” represents molarity in chemistry.
- Molarity is commonly expressed in units of mol/L (moles per liter).
For example, a solution labeled as 0.1 M contains 0.1 moles of solute in 1 liter of the solution.
What is Mole
In the table above we refer to a new name (mol). Mole is defined as the quantity that contains exactly 6.02 * 10**23 elementary entities, such as atoms, molecules, or ions. This number (6.02 * 10**23) is known as Avogadro’s number.
