[antoniolugo]

How can I stabilize phosphoric acid to mix with calcium?

I know I can stabilize the phosphoric acid with potassium hydroxide but I still cant get it to mix with liquid calcium. Once mixed it looks ok but after 2 to 3 days I can see some precipitate on the bottom of the glass.

Thanks

[Borek]

I am afraid you got it all wrong.

When you add potassium hydroxide to phosphoric acid you don't stabilize it - you neutralize it, converting it to completely different compound.

What is a liquid calcium? The only thing that comes to mind is a melted metal, but I doubt that's what you mean. Most likely you mean some solution containing calcium ions. Calcium phosphate is weekly soluble, no wonder you see a precipitate. It can be possible to do something, but it depends on what your application is.

[antoniolugo]

The liquid calcium is made of calcium nitrate.

Im trying to make a solution that can have calcium and phosphate in liquid form as a nutrient solution for plants in a experiment with tomatoes.

I used the wrong word by saying stabilizing it, I should of said neutralizing it, because of the charges and the phosphate becoming potassium phosphate with the hydroxide. After this reaction is done I would let it cool for a day and then add the liquid calcium.

I hope you get a better idea.

[Borek]

If you want both ionic PO₄^3- and Ca²⁺ to be present in the solution, you can't avoid precipitation, until the solution will be quite dilute.

[antoniolugo]

So you are saying that in concentrated form there will be a little some precipitate, but as I dilute it with water the residue will dissolve as well?

[Borek]

Something like that.

Note that solubility of calcium phosphate is quite low, around 0.002 g per 100 g of water.

[antoniolugo]

I can see that after diluting it it the residue does dissapear.

But is there a way to prevent the formation of calcium phosphate? Having the phosphate convert to another compound but leaving the calcium alone?

[Arkcon]

No, this can't be avoided by some sort of treatment.  I'm going to assume that you're making hydroponic nutrient solution (if you're not, the obsession with soluble nutrients makes the answer the same.)  Here's a page with a formula -- http://busiweb.tripod.com/hydro/juice.htm  And you'll be able to find others.  Basically, you'll use another salt as the source of phosphorus, one that doesn't react with calcum to form an insoluble compound.

[antoniolugo]

Yes I am making a hydroponic solution.

Thanks I will check that page up!

[curiouscat]

Basically, you'll use another salt as the source of phosphorus, one that doesn't react with calcum to form an insoluble compound.

If Ca²⁺ and PO₄^3- form  a ppt at a certain conc. (dictated by their solubility product); won't they always form it? How does changing the counter-ion (I assume that's what changing the salt means?) help?

Not doubting your advice at all; just wondering about the fundamentals.

[Borek]

"Another salt" doesn't have to mean phosphate.

Not that I have a better ideas.

[antoniolugo]

I havent found other P salts that dont react with Ca. Mono Potassium phosphate also reacts with Ca.

[Arkcon]

Its possible that, by using the mono- and di- basic salts, you can get a pH that inhibits precipitation, at least at the low levels of ions that the nutrient solution is kept for plant growth.  Perhaps the calcium phosphates are dispersed as very fine precipitate that plant roots can collect and absorb as they need it.  The dilemma you may be facing is your stock solution, at higher concentration, is precipitating.  Often, you see hydroponic stock solutions in two or more parts stored separately, that are then mixed with water to the concentration plants need, often with separate additions of pH adjusters.