# Which salts can be used to precipitate chloride ions? [closed]

We don’t have AgNO3 in the lab. I have no idea what else can be useful. I am washing a product and I want to make sure the chlorides are washed away.

## closed as too broad by Todd Minehardt, airhuff, Nilay Ghosh, M. Farooq, TyberiusJun 19 at 16:16

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• AgNO3 is not really used to wash products. You remove the chloride ions by precipitation but you replace them with nitrate ions, and the sodium ions are still there too, so the product would still be impure. – IanC Jun 17 at 19:22
• Well, Lead(II) nitrate is an option, it precipitates in the cold, and dissolves upon heating. But even in the cold it is far more soluble than AgCl, so this is not a very sensitive method. You can concentrate the solution beforehand. But why have you no AgNO3, and why don't you just buy some? It's not really expensive. – Karl Jun 17 at 19:43
• Hg(I) cations would also precipitate as Hg2Cl2, their low solubility is the whole idea behind Group I of cation analysis. But then again, it wouldn't be really washing a product since you'd be only removing the chloride ions and replacing them with whatever anion you had on your added salt. Not sure what is the OP goal. If it's removing only the chloride because of some reaction interference then I think it's fine, but as product purification this doesn't sound much useful.. – IanC Jun 17 at 19:51
• @IanC OP wants to check if he washed his product chloride-free, by testing the water with silver nitrate. At least that's what he says, and it's a very common procedure. ;-) – Karl Jun 17 at 20:06
• Then the OP wants to detect chlorides in truly minor amounts, and neither Hg(I) nor Pb are good for that. – Ivan Neretin Jun 17 at 20:13

## 2 Answers

The only well known method to check for (the absence of) chloride ions is precipitation as AgCl (solubility 2 mg/l at 20°C).

Mercury(I) chloride is similarly badly soluble, but toxic (and unstable, disproportionation) and therefore bad practice.

Lead(II) chloride is already far more soluble (4 g/l) than AgCl, and practically all other simple chlorides are just very well soluble in water.

Silver nitrate is cheap, the internet sells 10 g high purity $$\ce{AgNO3}$$ for 25€. Just get some.

Another option could be a ion selective electrode (ISE) selective for chlorides, but it would make sense rather for regular checks, as there would be high one time investment.

The principle is the same as for the potential reference electrode ... $$\ce{Ag | AgCl | KCl}$$ ... but this time with mono or polycrystallic $$\ce{AgCl}$$ exposed to the solution. It is usually integrated with a true reference electrode, forming the complete cell with the voltage dependent of $$\ce{Cl-}$$ activity.