Measure COD, mask chloride ions, final mercury chloride content
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15,000 chloride ions; 3 ml of water sample is used, along with 3 g of mercury sulfate – how much mercury chloride is produced in the end?
Because it has precipitated, it cannot be expressed in g/L!
So how should that be expressed, or how is it calculated?
Moreover, mercury chloride is also soluble in water, with a solubility of around 6-8 g
As for how much mercury chloride should be produced, it also needs to be determined based on the amount of chloride ions remaining in the water~since complete precipitation is not possible.
According to the national standard GB11914, this is done to form stable chloro-mercuric complexes thereby preventing interference in the tests. So the “amount of mercury chloride produced” is not important; there’s no need to worry about it. Empirical data suggests that 0.4 g of mercuric sulfate is required to mask 40 mg of chloride ions.
1. Mercury is definitely in excess. 2. Generally, the calculation is based on the total amount of ligands; for example, with 2,000 chloride ions, 10 g of mercury is required. Then can the mass of the resulting complex ion HgCl4²⁻ be calculated in terms of mass?
If one insists on going down this path, one should look up the solubility product constant; if that’s not available, then one can consult relevant papers or other sources for the necessary parameters. If you are sure that you have the necessary experimental conditions, you can also design your own test plan and conduct tests for verification.