Drinking natural mineral water (physical and chemical) testing

10 Total Acidity 10.1 Principle Acidity is the quantitative ability of water medium to react with hydroxide, determined quantitatively by titrating a certain volume of water sample to a certain pH using a strong alkaline standard solution. The measurement results are expressed in mg/L, which is equivalent to the content of calcium carbonate (CaCO). The numerical value is related to the pH of the selected titration endpoint. This method uses phenolphthalein as an indicator, with an endpoint pH of 8.3, and the measured acidity is called total acidity. 10.2 Reagents and Materials Unless otherwise specified, all reagents used in this method are analytical pure, and the water is Grade III water as specified in GB/T 6682. 10.2.1 Carbon dioxide free water: Boil the water for 15 minutes and then cool to room temperature without contact with atmospheric carbon dioxide. The pH of this water should be greater than 6.0, otherwise the boiling time should be extended. It is best to prepare it in time. 10.2.2 Sodium hydroxide standard solution [c (NaOH)=0.05 mol/L]. 10.2.2.1 Preparation Weigh 20 g of sodium hydroxide, dissolve in 100 mL of water, shake well, transfer to a polyethylene bottle, seal and place until the solution is clear. Suck 10 ml of the upper clear liquid and inject it into a polyethylene bottle containing 1000 ml of water, and store it tightly. 10.2.2.2 Calibration Weigh 0.2 g to 0.3 g (accurate to 0.000 1 g) of potassium hydrogen phthalate (KHC, H2O, reference reagent) dried to constant weight at 105 ℃ to 110 ℃ in a 250 ml conical flask. Dissolve in 50 ml of water, add 4 drops of phenolphthalein indicator, and titrate with the prepared sodium hydroxide solution until pink. Simultaneously conduct a blank test

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