，
The pH value of water is a valuable indicator of water quality. It is the basic parameter for understanding and evaluating the chemical composition of water sources, the organic pollution load and the capability of water to corrode metal objects. The pH of water can also be indicative of biological conditions, as certain microorganism are available at certain pH levels.
The pH of aqueous solutions is determined with glass electrodes and can be obtained in terms of a relative value. According to the Chinese Technical Standard GB 6920-86, the pH value of water is measured with a glass electrode. A determination of the pH value of an aqueous solution requires the use of a reference electrode, usually a saturated calomel electrode (SCE). The electrodes are placed in sand or asbestos to avoid contact with the walls of the vessel and potential contaminants. The potential of the glass electrode is measured directly against the reference electrode. A pH meter measures the potential of the glass electrode relative to the reference electrode and converts it to a pH value.
In order to obtain reliable and accurate results, it is important to follow the correct procedures while performing the acidity measurement. The cells should be freshly calibrated and re-calibrated with a standard solution in between different samples. The pH of the buffer and standard solution must be checked before the measurements are carried out. The pH meter must be regularly checked for its accuracy and for any zero balance errors. The glass electrodes should be carefully washed, rinsed and cleaned before and after each use.
When measuring the pH of aqueous solutions, it is important to take environmental factors into account. For instance, fluctuations in temperature can cause errors in the pH measurements. High temperature can cause the pH measurement to be higher than the actual value and low temperatures can give a lower pH value. This can be avoided by performing all the measurements at a fixed temperature.
For most water quality measurements, the pH level is high enough that the average value of the range between 5 and 9 will reasonably represent samples of the same water body. However, in areas with waters that are expected to vary greatly in pH, or where the influence of agricultural activities or other sources of acid or alkaline material is expected, the pH should be determined with greater precision. Measurement of total alkalinity helps to interpret the results and ascertain the contribution of natural and anthropogenic sources to changes in alkalinity.
The pH is an important parameter for the health of aquatic species, as the toxicity of some substances depends on pH. Thus, accurate pH measurement is essential for determining the health of the aquatic habitats. The pH of the water is also required for accurate measurement of water treatment parameters such as chlorine, bromine, and other chemical concentrations.
In conclusion, GB 6920-86 should be strictly followed to accurately determine the pH of aqueous solutions using glass electrodes. The pH measurements should be performed after taking environmental factors into account and with regular calibration of the instruments for optimal accuracy. This information is important for assessing and monitoring the aquatic habitat as well as optimizing water treatment processes.
