Soluble or insoluble??

Question

I recently did a lab on creating a Liquid Fertilizer in my Chem 231 class and we used the compounds...

KNO3, Na3PO4, KCl, and Fe(NO3)3 which were added into water

When all compounds were added into the flask with WATER it was insoluble. I have searched the solubility table and it shows they should all be soluble.

So which is the cation and which is the anion?? And how do I determine what the solid created was?

pisgahchemist · Accepted Answer

Insoluble compound.....

When you combine all of the cations (positive ions) and anions (negative ions) from soluble solutions of KNO3, Na3PO4, KCl, and Fe(NO3)3 you have cations of K+, Na+, and Fe3+, the NO3^-, Cl- and PO4^3- anions.  when all of these ions interact with each other, one pair will form an insoluble compound: the Fe3+ cation and the PO4^3- anion, and insoluble FePO4 will be the result.

Fe3+ + PO4^3- --> FePO4(s)

Indeed, all of the original compounds are soluble, but you have to look at all of the possible products to see if any of those are insoluble:

KCl, NaCl, FeCl3, KNO3, NaNO3, Fe(NO3)3, K3PO4, Na3PO4, FePO4

Some of these are duplicates of the reactants, and of course FePO4 is the insoluble product.

Roger the Mole · Answer

Salts of K and Na are usually soluble, so Fe is the likely trouble-maker.
Iron salts of NO3 and Cl anions are soluble, so the problem is almost certainly FePO4, which is nearly insoluble.

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Soluble or insoluble??

2 Answers