Josh~ Superphosphate is used instead of just phosphate because superphosphate is a compound whereas phosphate is an ion. This means that phosphate must attach itself with a cation in order to give a plant its phosphorus supplement, it could do this by attaching itself to 3 calcium to make tribasic calcium phosphate but that is insoluble in water and Plants can only absorb materials when they are dissolved in water. In chemistry ‘like dissolves like’ so nonpolar solutes can only dissolve in nonpolar solvents, water is polar and tribasic calcium phosphate is nonpolar so phosphate cannot dissolve in water. This is why Superphosphate is so great because it has phosphorus and it can provide it because it is soluble.

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    $\begingroup$ You seem to be in some fundamental disagreement with our reality. You've asked this before, and the answer is not going to change, no matter how much you dislike it or how many times you repeat the question. Being soluble or insoluble is simply not a property of ions. Then again, in my book phosphate is definitely an ion; maybe you are using this word to denote something entirely different? $\endgroup$ Aug 5 '19 at 5:38

Ions are always dissolved in their solution. Anything that has charge is an ion. If phosphate ions are present in a solution it is because they came from a soluble parent molecule such as phosphoric acid.

  • $\begingroup$ Thanks for you answer, Can you give plants phosphate (PO4 3-) instead of super phosphate for their phosphorus supplement? $\endgroup$ Aug 5 '19 at 4:48
  • $\begingroup$ When you give a plant super phosphate you are giving it monnoammonium phosphate salt. You can't get "just Phosphate ions" by themselves, it's likely that some other salts of phosphate would work and that others would kill your plant. $\endgroup$
    – Josh
    Aug 5 '19 at 5:26
  • $\begingroup$ Thank you so much, you mean monocalcium phosphate right? $\endgroup$ Aug 5 '19 at 5:27
  • $\begingroup$ I was looking at a bag that used monnoammonium phosphate, you must be looking at one that uses monocalcium phosphate. What the plant needs is phosphate and various cations bound to the phosphate may work. $\endgroup$
    – Josh
    Aug 5 '19 at 5:33
  • $\begingroup$ Thanks so much for you help, you've helped me in more ways than you can imagine. If you dont mind can you tell me if this paragraph makes sense in respect to Chemistry. I put it in the description under your name. I really appreciate your help. $\endgroup$ Aug 5 '19 at 5:55

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