Ca(H2PO4)2 + NaOH(limited) → CaHPO4 + ?

[Bohrok]

This is a problem I was trying to help some chem students with. This is all that was given.

Ca(H₂PO₄)₂ + NaOH(limited) → CaHPO₄ +

Will one hydrogen be neutralized on each dihydrogen phosphate to yield Na₂HPO₄ and water? This is my guess so that the two phosphate ions stay the same/get the same neutralization. It's hard to say what those four hydrogens and limited NaOH would actually make...

Ca(H₂PO₄)₂ + 2NaOH(limited) → CaHPO₄ + Na₂HPO₄ + 2H₂O


They had another problem that was exactly the same but had Mg in place of Ca. Would that reaction be the same?

 

[Borek]

Seems logical to me. CaHPO₄ is weakly soluble, so it can easily precipitate. Ditto for MgHPO₄.

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[Bohrok]

Just remembered that the problem said the Ca(H₂PO₄)₂ and CaHPO₄ were solid, and Mg(H₂PO₄)₂ and MgHPO₄ were aqueous. I suppose that doesn't affect the first one, but what about the second one with the Mg?

 

[Borek]

Ksp for CaHPO₄ is 6.58 and for MgHPO₄ 5.82 - this is not a large difference, so I don't think they should behave differently. Unless we are talking about some fancy geochemical reactions.

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methods

 

[Bohrok]

This is just introductory chemistry, so nothing too complicated.
Thanks for your response.