The pH scale is a measure of the acidity or basicity of a substance, and it ranges from 0 to 14. The pH scale was developed as a way to quantify the acidity or basicity of a substance based on the concentration of hydrogen ions (H+) in the solution. The pH scale is logarithmic, meaning that each increment on the scale represents a tenfold difference in acidity or basicity. A substance with a pH of 4 is ten times more acidic than a substance with a pH of 5, and a substance with a pH of 9 is ten times more basic than a substance with a pH of 8. The pH scale was designed to cover a wide range of acidity and basicity, from highly acidic substances with a pH of 0 to highly basic substances with a pH of 14. The pH scale is useful for measuring the acidity or basicity of substances in a wide range of applications, including food, medicine, and industrial processes. It is important to note that the pH scale is a measure of the acidity or basicity of a substance and does not directly reflect the concentration of H+ ions in the solution. The concentration of H+ ions in a solution can be calculated using the pH of the solution and the equation: pH = -log[H+] This equation can be used to convert between the pH of a solution and the concentration of H+ ions in the solution.