【Daily Question】Chemical Analysis Version 2021.10.19
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When determining SO42- using EDTA, the method to be employed is: A. Direct titration B. Indirect titration C. Back titration D. Continuous titration D
Let’s discuss this: EDTA is generally used to determine sulfate levels in water samples. A certain amount of a barium-magnesium mixed standard solution is added (magnesium serves to increase the sensitivity of the indicator), and the sulfate content in the sample is calculated indirectly by comparing the volume of reagent added to the blank sample with that added to the sample itself. So it can be called indirect titration, back-titration. However, when the sample itself contains substances that can react with EDTA, it is possible to titrate to the endpoint first and then add the standard solution; this seems to be continuous titration. The answer is D, which is reasonable; choosing BC is not necessarily wrong either.