Solution pH and acidity meter
At the middle school stage, we heard the teachers say that the PH test paper is used to test the acidity and alkalinity of the solution. When the test paper touches the solution, it will change color, and then read the PH according to the color. It was particularly magical at that time.
In the actual testing process, the accuracy of the PH test paper is far from enough, so how can I get the PH value of the solution more accurately?
Then we must rely on the PH meter we are talking about today. Yes, it is also called a pH meter!
Instrument introduction
Chinese name ph meter, also known as acidity meter
Foreign name PH meter
Measuring range 0-14PH
Supply voltage AC220V
Output 4-20ma, RS485 and other signals
Temperature resistance level 0-130 degrees Celsius
Instrument principle
PH meter
A pH meter, a pH meter, is an instrument used to determine the pH of a solution. The sensor uses the electrochemical properties of the solution to measure the hydrogen ion concentration to determine the pH of the solution. The negative value of the logarithm of the hydrogen ion concentration is called the pH value. Usually, the pH is 0 to 14. The pH of the neutral water at 25 ° C is 7, the solution having a pH of less than 7 is acidic, and the pH is greater than 7 is alkaline. Temperature has a large effect on the ionization coefficient of water, and the neutral point causing the pH changes with temperature. The principle of pH measurement by the pH meter is to establish the relationship between the ion activity and the electromotive force by using the potential analysis method, and measure the pH value by measuring the current of the primary battery.
Precautions
The glass electrode must be soaked in distilled water for more than one night before it is used for the first time. It should also be soaked in distilled water for use at any time. Do not touch the glass electrode with strong water-absorbing solvent for too long. Use it in a strong alkali solution as soon as possible. Wash it with water immediately after use. The glass electrode bulb is very thin and cannot be touched with glass and hard objects. When oil is contaminated, use alcohol, then carbon tetrachloride or ether, and finally soak in alcohol, then wash with distilled water. When measuring the pH of a protein-containing solution, the surface of the electrode is contaminated with protein, resulting in unreliable readings, instability, and errors. The electrode can be immersed in dilute HCl (0.1 mol/L) for 4-6 minutes to correct it. . After cleaning the electrode, you can only use the filter paper to dry it gently. Do not wipe it with a fabric. This will cause the electrode to generate static charge and cause reading errors. When the calomel electrode is used, be careful that the electrode is filled with potassium chloride solution, and there should be no air bubbles to prevent open circuit. A small amount of potassium chloride crystals should be present to keep the solution in a saturated state. When using, the rubber plug on the top of the electrode is removed, and a small amount of potassium chloride solution is discharged from the capillary to make the measurement result reliable.
In addition, the accuracy of the pH measurement depends on the accuracy of the standard buffer. Standard buffers for acidity meters require greater stability and less temperature dependence.
