What is pH meter?
Water pH concentration of hydrogen ions acidity Or determines whether it is alkaline. Pure water decomposes to a very small extent into H and OH ions. The pH of drinking water should usually be around 7 (neutral). In case of pH less than 7, water becomes acidic and in case of pH above 7, water becomes alkaline.
The lower the pH of water than the neutral pH of water, the higher the solubility of iron in water, so in different industries to prevent water corrosion,PH of water The corrosion rate due to the acidity of the water increases with increasing temperature, so it is absolutely necessary to keep the pH of the water high at high temperatures.
The pH of contaminated water is essentially the relationship between carbon dioxide Free and shows the amount of bicarbonate and carbonate. Natural waters usually have a pH between 4 and 9. And most of them are slightly alkaline due to the dissolution of carbonates and alkaline bicarbonates of the earth’s crust.
Different methods of PH measurement:
There are two general methods for measuring the pH of water, which include the following two methods.
- How to use an electric PH meter
- Determination of pH by colorimetric method
Electric pH meter:
Most pH measurements in the laboratory are performed using an electrical circuit using a pH meter. The circuit consists of a glass electrode and an external reference electrode and a voltmeter that records the electrical potential in the circuit. . The glass electrode consists of a current-carrying wire that is immersed in a solution with a specific pH.
Calibrate PH meter:
The device must be calibrated before using the pH meter. Buffer solutions with known pHs are suitable for this purpose.
Turn on the pH meter, wash the electrode with distilled water and shake it to dry. Then we put it in a human containing a buffer solution with pH 7 and wait for the number to be fixed on the screen.
Wash the electrode with distilled water and shake it well to absorb the water. Then place it in the buffer solution with pH 4 so that the pH of the meter is stable.
The calibration of the device is controlled by measuring at a standard pH of 7. To do this, the electrode must be placed inside the solution.
At this stage the PH meter is ready.
At this stage, pour a sufficient amount of sample into a human 100 ml and immerse the electrode in it and leave the device to not be stable for about 2 minutes, when the number is fixed on the device, the pH value of the sample sample from the screen We read the comment.
Tips on how to maintain the pH electrode:
The important thing about using a pH electrode is to avoid placing it in solutions that react with silver.
If you put the pH electrode in distilled water for a long time, because the electrode contains KCl and the distilled water does not have it, the KCl in the electrode will gradually enter the distilled water and of course it will disrupt the work of the electrode.
PH electrode glass membrane cleaning:
If the electrode does not accurately display the pH of these buffers, one of the reasons may be contamination of the electrode glass membrane.
To clean the electrode glass membrane, soak the tip in 0.1 M hydrochloric acid solution for 15 seconds and then rinse with distilled water. Then soak it in 0.1 M solution
Leave on for 15 seconds and rinse with distilled water after 15 seconds. Repeat these actions several times.
Now check the pH of the buffers again. If the problem persists, soak the tip of the electrode in 20% ammonium fluoride solution for 30 seconds or in 10% hydrofluoric acid solution for 15 seconds. Then rinse with distilled water. Next, soak the electrode tip in concentrated hydrochloric acid for 30 seconds (this is to remove any possible fluoride residue from the glass membrane) Then rinse well with distilled water.
Place the electrode in the buffer for one hour at pH = 4. Then test the electrode. If the problem persists, you will probably need to replace the electrode.
PH meter by colorimetric method:
This chemical method used to determine the pH is to add a drop of an acid-base indicator to the sample. The pH indicator papers are suitable for this purpose. A drop of the sample is placed on the pH paper. Indicators are observed. Indicators are large organic molecules that change color based on the pH of the solution. Color change is observed within a range of pH range for each indicator (usually about 1.5 pH units). Medium pHs are seen in the middle of the table. Based on this pH value, intermediate colors are also in this pH range.
For example, a red cresol indicator at a pH below 7 is the color of the indicator solution yellow, and at a pH above 8.8 the color of the solution is red. At moderate pH values, depending on the type of pH, the color change of the solution will be orange.
There are many different indicators that can cover the entire pH range.
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