Why are the methods for preparing the buffer solutions used in hardness measurement different?
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There are several ways to prepare the pH=10 buffer solution used in the EDTA titration method for measuring water hardness, and the concentrations vary greatly. Does this have an impact on the results? In what scopes does it apply? For example: In GB/T 603-2002, 4.1.3.3.1 Ammonia-ammonium chloride buffer solution A ((pH 10)): Weigh 54 g of ammonium chloride and dissolve it in water; add 350 mL of ammonia water, then dilute to 1000 mL. Ammonia-ammonium chloride buffer solution, type B (pH 10): Dissolve 26.7 g of ammonium chloride in water, add 36 mL of ammonia water, and dilute to 1000 mL. According to GB/T 6909-2008, dissolve 67.5 g of ammonium chloride in 570 mL of concentrated ammonia water, add 1 g of magnesium disodium EDTA salt, and dilute with water to 1 L. There is also one prepared with 20g of ammonium chloride; how should one distinguish which to use?
1. Select a weak acid with a pKa value close to the desired pH. 2. Calculate the ratio and concentration of conjugate acid-base pairs based on pH and pKa. ① React a weak acid with a strong base in a certain ratio to form a weak acid-weak base salt solution. ②Mix the weak acid with its corresponding weak acid salt in proportion. 3. Choose a weak base, as above.
Could you provide examples to illustrate the question I raised?
The preparation methods I have proposed are all ammonia-ammonium chloride buffer solutions, with a pH of around 10; the only difference is the concentration
Great stuff, I’ve downloaded it. Thank you