The alkalinity of water refers to the amount of water containing substances that can accept hydrogen ions, such as hydroxide, carbonate, bicarbonate, phosphate, hydrogen phosphate, silicate, hydrogen silicate, sulfite , Humate and ammonia are all common alkaline substances in water, and they can all react with acids. Therefore, by selecting an appropriate indicator and titrating them with a standard solution of acid, the alkalinity in water can be measured Content.
Alkalinity can be divided into phenolphthalein alkalinity and total alkalinity. Phenolphthalein alkalinity is the amount measured when phenolphthalein is used as an indicator, and the pH of its end point is 8.3; full alkalinity is methyl orange as an indicator At the time of measurement, the pH value of the end point is 4.2. If the alkalinity is very small, methyl red-methylene blue should be used as an indicator for the total alkalinity, and the pH value of the end point is 5.0.
Determination of hardness (content of calcium and magnesium in water) (EDTA titration method)
In the test solution with a pH of 10.0 + -0.1, using chrome black T as an indicator, titrate the standard solution of ethylenediaminetetraacetic acid disodium salt (EDTA) to blue as the end point, according to the volume of EDTA standard solution consumed , You can calculate the hardness content in water.
Temporary hardness is also called carbonate hardness, and permanent hardness is also called non-carbonate hardness. General hardness and alkalinity can be calculated as calcium carbonate.
When total hardness> total alkalinity, carbonate hardness = total alkalinity, non-carbonate hardness = total hardness-total alkalinity.
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