hodges - 27-9-2019 at 13:29
I dissolved 1g of ferric ammonium citrate in a small amount of water (few ml).
Likewise, I dissolved 1g of calcium chloride in a small amount of water (few ml).
I mixed the two. Since both calcium and citrate ions are present, and the solubility of calcium citrate is less than one gram per 100ml of water, I
would have expected to see a precipitate of calcium citrate. But no precipitate, and no visible changes at all. Why?
DraconicAcid - 27-9-2019 at 13:47
Because the citrate is coordinated to the iron(III) ions and won't let go. If you add sodium hydroxide, you will also not see any iron(III) hydroxide
forming.
hodges - 28-9-2019 at 12:42
I tried adding NaOH solution to the mixture. At first, I get a gray precipitate. This might be the calcium citrate I was looking for, but it might
also be a mixture of iron and calcium hydroxides. As I continue to add more NaOH, the precipitate becomes brown, and appears to be iron(III)
hydroxide.
Also tried adding NaOH solution to just the ferric ammonium citrate. I get a brown precipitate only, likely iron (III) hydroxide, and I do smell
ammonia.