What is the pH scale?
pH measurement is a relative measurement, which only indicates the pH difference between the standard solution and the unknown solution. During actual measurement, it needs to be calibrated regularly with a standard buffer solution. Therefore, in order to achieve consistent values, a pH scale must be established. The pH scale range is set from 0 to 14 pH, and the value of the pH scale is determined by the pHs value of the reference buffer solution. Therefore, the meaning of the pH scale can be expressed as: according to the definition of pH, select several pH buffer solutions in the range of 0 to 14 pH as fixed points of the pH scale, and measure their pHs using accurate methods that can be achieved with contemporary technology. . There are two types of pH scales in the world, namely multiple base pH scales and single base pH scales. China uses multiple base pHs scales. The pHs values of the six reference buffer solutions from 0 to 95°C are shown in Table (1).
Does pH measurement require calibration?
There are usually two types of pH measurement: colorimetric method (pH test paper or cuvette) and electrode method. Of course, the colorimetric method does not need to be calibrated, but the electrode method must be calibrated, because the electrode method pH measurement is to compare the unknown solution with the standard solution with known pHs value in the measuring cell. This is the "operational definition" of the electrode method pH measurement. "Decided.
What is water pH? What's the point?
PH value is one of the important physical and chemical parameters of aqueous solution. All natural phenomena, chemical changes and production processes involving aqueous solutions are related to pH value. Therefore, pH value needs to be measured in the fields of industry, agriculture, medicine, environmental protection and scientific research. The pH value of water is the negative logarithmic value of the hydrogen ion activity in the water, expressed as: pH=-lgaH+ The pH value is sometimes also called the hydrogen ion index. Since the value of hydrogen ion activity is often very small, it is very inconvenient in application. Therefore, the concept of pH value is used as an indicator of the acidity or alkalinity of an aqueous solution. Moreover, the negative logarithmic value of hydrogen ion activity can express the magnitude of the change in acidity and alkalinity, which is very convenient to apply, and thus we can obtain: (1) Neutral aqueous solution, pH=-1g aH+= -1g 10-7=7 (2) Acidic aqueous solution, pH7, the greater the pH value, the stronger the alkalinity.
