pH meter, Construction, advantages


What is pH?

The pH (hydrogen ion potential) of a solution is defined as pH = - log10 (H +), where (H +) is the concentration of hydrogen ion. The pH scale (of the hydrogen potential) is the logarithm of the reciprocal of the concentration of hydrogen ions in gram atoms per liter and provides a measure on a scale of 0 to 14 of the acidity or alkalinity of a solution (where is neutral and greater than 7 is more basic and less than 7 is more acidic).

Construction of a pH meter:

There are all kinds of pH meters; Some are used to test the pH of the soil, the water in the pool and even the wine. They come in different sizes and shapes. The following is the basic construction of a pH meter:


A basic pH meter consists of a specially developed measuring probe (electrode) that is connected to an electronic meter that shows the pH reading. There are two main types of electrodes: the glass electrode and the reference electrode:

Glass electrode:

This is the simplest and most common electrode. It consists of a sturdy glass tube with a thin glass bulb welded to it. Inside there is a known solution of potassium chloride (KCl) buffered to a pH of 7.0.
The silver electrode with a silver chloride tip makes contact with the internal solution. To minimize electronic interference, the probe is protected by a blade protector, which is often located inside the glass electrode.

Calomel reference electrode:

It consists of a cavity containing mercury and calomel (Hg2Cl2) that are in contact with each other. The contact between the mercury and the calomel is carried out by means of a platinum wire, while the small inner chamber is surrounded by a solution of saturated KCl.

The contact between the saturated KCl and the measured solution, the liquid connection, is made through a porous ceramic pin. The potential produced at this point is constant and is determined by the solubility product of the calomel and the concentration of the KCl solution.

The potential of the reference electrode system is defined by the reference electrolyte and the reference element (e.g., silver chloride). Here it is important that the reference electrolyte has a high concentration of ions, which results in a low electrical resistance.

Advantages of having accurate pH control:

  • manufacture a product with defined attributes
  • produce a product at low cost
  • prevent damage to the environment, materials and humans
  • satisfy legal regulations
  • gain further knowledge in research