How does the pH meter measure the pH value of groundwater?
1. Measuring principle
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pH is one of the most important and frequently performed analysis items in water analysis, and is an important parameter for evaluating water quality. Contaminated water can cause large changes in pH. When the water contains a large amount of free carbon dioxide, the pH value of the water can be significantly lowered.
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In this method, the pH glass electrode is used as the indicator electrode, and the saturated calomel electrode is used as the reference electrode, which is immersed in the measured solution to form a primary battery. At 25°C, each unit of pH is equivalent to a change in electromotive force of 59.1mV. That is, every time the electromotive force changes by 59.1mV, the pH value of the solution changes by one unit. After positioning with the standard buffer solution, put the electrode into the sample, and the pH value can be read directly on the pH meter. The temperature difference can be corrected by the temperature compensation device on the instrument. The color, turbidity, colloidal substances, oxidizing agents, reducing agents and higher salt content of the water samples do not interfere with the determination. However, in a strong alkaline solution, when there is a large amount of sodium ions, an error will occur, making the reading low.
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2. Required reagents
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Unless otherwise specified, the reagents used in this method are reference reagents or pH buffers, and the water is distilled or deionized water.
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Preparation of pH standard buffer solution: Weigh the specified amount of reagent into the burning standard, dissolve it with deionized water, transfer it to a 1000mL volumetric flask, and when the temperature reaches 25°C, dilute with water to the mark and shake well. The deionized water used should be boiled to remove carbon dioxide before use, and then used after cooling. The conductivity of the deionized water should be less than 2μs/cm, and the pH should be between 5.6 and 6.0.
