The functioning of the pH meters is different in each model, although in general they follow a very similar process to provide the most accurate results, which is very important since the pH scale varies in an algorithmic function where a brief variation can represent up to twice as much acidity or alkalinity.
How Does a PH Meter Work
In general they work with a glass sensor and a reference tube. Also, a pH probe that measures the activity of hydrogen ions through a process that generates a small amount of voltage between the sensor and the reference tube. The voltage is measured as an electric current and the voltage generated in this current is converted into a pH value that is displayed on the digital display of the meter. In this way, multiple measurements of any liquid, semi-solid or solid that is required can be made.
Some models of pH meters include a function called automatic temperature compensation. To perform this function include, in addition to the mentioned components, a thermometer that automatically adjusts any discrepancy generated by the temperature to a baseline of 25 ° C. For the correct reading of any model must perform a calibration of the device, In this way, erroneous readings will be avoided.
The pH of a solution can not only be determined using acid-base indicators. It can be determined equally and even more precisely by electrochemical means. For this it is important to choose a half cell reaction which is directly dependent on the H + ion concentration. However, the necessary reference electrode must not be dependent on the pH value so that measurement by electrochemical means leads to success. For such measurements, the hydrogen half-cell is suitable as a pH-dependent cell, however, a glass electrode is chosen for ease of handling. It consists of a very thin glass membrane (0.001 mm) which is filled with a buffer solution with a certain pH. The actual electrode is a platinum wire.
The reference electrode is in most cases a silver-silver chloride half-cell. In principle, however, a calomel electrode would also be suitable. It consists of a potassium chloride solution (c (KCl) = 0.1 mol / l) and a solid precipitate of silver chloride. In it, a fine silver wire dives. Due to the solubility product and the defined chloride ion concentration, a defined silver ion concentration is established. This results in an electrode potential of E (Ag + / Ag) = 0.2814V.
If the measuring system is immersed in an acid or base solution, H + ions diffuse through the glass membrane. The amount of diffusing H + ions depends on the pH of the sample solution. Thus, a pH-dependent potential is formed between both sides of the glass membrane.
Using a voltmeter, a potential difference between the glass electrode and the reference electrode can now be measured. This gives a reading in volts. The pH meter now has a computing chip , which can calculate back to the H + ion concentration via the Nernst equation . This gives a value in pH units.
To make the best use of
For your pH meter to work in the best possible way, it is important that it has a calibration certificate. Most models can already be purchased with this certificate. However, after a period of use, it is necessary to look for a laboratory that re-calibrates, as indicated by the manufacturer, or if it presents problems, ensuring that the accuracy of the measurements is not impaired.
N addition, the pH meter should be calibrated during use with standard pH solutions, which usually accompany the apparatus. The tip is to choose one with the standard pH 7 and another with the value close to what is expected of the sample. Place a portion of the solution in a container and immerse the electrode in it, then do what is indicated in the specific instructions of your meter. This process is essential but straightforward since you will understand the accuracy of the readings so that you make adjustments if necessary.