Have you ever wondered what makes a lemon sour or why baking soda can be used as a cleaning agent? The answer lies in the pH scale, a measure of acidity and alkalinity.

The pH of a substance can be measured using a pH meter which measures the voltage difference between two electrodes and converts it into a pH value, or with pH paper which changes color according to the acidity or alkalinity of the substance it is dipped in.

  • The pH scale is a precise way of classifying the acidity, basicity, or neutrality of any solution.
  • The pH scale is a numerical and a visual scale, that can be represented by numbers, graphics, and colors.
  • The numerical scale has values ranging from 0 (the most acidic) to 14 (the most basic).
  • Pure water has a pH value of 7. This value is considered neutral (neither acidic nor basic).

The Maths Behind pH Scale

The pH scale is a logarithmic scale of base 10, so each pH unit is ten times stronger than the one above it, or ten times weaker than the one below it. For example, a solution of pH=3 is ten times more acidic than s solution with pH=4, but ten times weaker than pH=2.

The term pH stands for (power of hydrogen) and refers to the involvement of the hydrogen ions based on the reactivity potential of the solution, whether it is a proton acceptor (base) or a proton donor (acid).

The pH scale is continuous and precise where decimal numbers and whole numbers can be used.

Detailed pH Scale with examples

What does the pH scale measure?

It measures the potential of a solution to accept protons in the form of hydrogen ions. Thus, the basic or alkaline solutions have higher pH values because of their potential to accept hydrogen ions. But the acidic solutions already have high concentrations of hydrogen ions, this is why they have lower pH values.

The strength of an acid or base is measured by the tendency of its ions to dissociate completely in an aqueous solution. This is measured by the dissociation constant, which is the ratio between the ions and the molecular form of the dissolved substance. The base yields hydroxide negative ions (HO), whereas acid yields hydrogen positive ions. (H) calculated based on the concentration (mol/l) of hydronium salt (H3O+)

In strong acids, the dissociation is 100%, once you get the concentration of hydronium ions in the solution you can directly apply the formula and get the PH.

pH = – log [ H3O+]

However, for weak acids, you can’t rely on the concentration of H3O+, you need to know the dissociation.

Digital pH scale

Concepts Berg

Why is pH logarithmic?

A logarithmic scale accommodates a huge range of numbers very easily, and since the concentration of H+ values varies over a wide range then the pH scale is a logarithmic function base 10 which means each order of magnitude is ‘only’ one digit in a log-to-base-ten scale, that is from pH= 3 to pH =2 means a 10-fold difference in H+ concentration

What should one know about the pH Scale?

pH is a measurement of acidity on a scale from 0 to 14. It tells us how acidic or alkaline a substance is. A pH of 7 is neutral and refers to water. Values below 7 indicate acidity and increase as the number decreases – making 0 the most acidic value. The pH scale is continuous and precise where decimal numbers and whole numbers can be used.
What is the use of the pH scale?

The pH scale is used to show whether a solution is acidic or basic, depending on the concentration of hydrogen ions.

What is the full form of pH?

The full name of pH is the power of Hydrogen.