Laboratory Technology pH-Value – What is it and How is it Being Measured?

The term "sour" has something to do with the so-called pH value: pH stands for pondus Hydrogenii, which means "weight of hydrogen", i.e. the concentration of hydrogen ions in a solution. The pH value therefore indicates how acidic (sour) or basic a solution is, with the most commonly measured values ranging from around 0 to 14. How the value is calculated, how its being tested and what it means exactly is explained in this article.

The pH value indicates how acidic or basic a solution is. PH stands for the Latin word ‘pondnus Hydrogenii’. This means ‘weight of hydrogen’, i.e. the concentration of hydrogen ions in a solution. These hydrogen ions are also called ‘protons’. If there are many protons in a b, it is acidic. If there are few protons, it is called alkaline/basic.

PH values are usually given on a scale from 0 to 14. Pure water has a value of 7, so a pH of 7 is ‘neutral’. A pH value less than 7 corresponds to an acidic solution and values greater than 7 are defined as basic or alkaline solutions.

Acidic solutions include, for example, Coca-Cola with a pH value of 4. The juice of a lemon is also defined as acidic. Soap water, for example, is an alkaline solution and has a pH value of approximately 9.

The calculation of the PH value

In the following calculation you can see, how the pH value is being calculated. The calculation is based on the amount of a specific substance in a liquid.

Measurement Devices

Indicator paper

A very simple and at the same time inexpensive method to determine the pH value are the pH test strips. These strips or sticks are simply held in the liquid to be measured and waited until the color no longer changes. The pH value can be read off from a color scale on the respective packaging. However, care must be taken.

pH meter

A pH meter can also be used to check liquids for their salt and acid content. For this purpose, a measuring technique with the glass electrode, which is also called pH electrode, is usually used. With this measurement, however, a variety of errors can occur, which falsify the result. Especially the electrode itself plays an important role.

The electrode must be selected to suit the liquid to be measured. With suitable electrodes, the reaction time of the test is approx. 30-90 seconds.

Relevant points for the selection of the suitable electrode are:

• Chemical composition

• Homogeneity

• Temperature range

• pH range

• Container size

For measurement, these conditions should be clarified in advance in order to find a suitable electrode. In this way, incorrect measurements can be avoided. Also, the calibration of a pH meter should not be neglected. Residuals from previous measurements can falsify the result without calibration.

All in one

In our article ‘All-in-One Optical pH & Oxygen & Temp Meter’ we already reported on a comprehensive all-in-one solution. The company Pyro Science developed a product that allows the measurement of several parameters. You can read all about the parameters and how they are measured in this article.

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