What are the products in the following reaction: #?Na_3PO_4(aq) + ?CaCl_2(aq) -> ?NaCl(aq) + ?Ca_3(PO_4)_2(s)#?

1 Answer
anor277
Jan 7, 2017

#"Calcium phosphate"# and #"sodium chloride"#. Of course there is speciation of the phosphate ion in aqueous solution.

Explanation:

Most phosphates are in fact biphosphates, i.e. salts of #["HPO"_4]""^(2-)#; this is certainly true in aqueous solution, where phosphate ion, #["PO"_4]""^(3-)#, is a powerful Bronsted base:

#"PO"_4""^(3-) + "H"_2"O" rarr "HPO"_4""^(2-) + ""^(-)"OH"#

In solution, your equation probably represents the reaction:

#"Na"_2"HPO"_4(aq) + "CaCl"_2(aq) rarr "CaHPO"_4(s)darr+2"NaCl"(aq)#.

If we keep with the equation as written, we get:

#"Na"_3"PO"_4(aq) + "3CaCl"_2(aq) rarr "Ca"_3("PO"_4)_2(s)darr+2"NaCl"(aq)#.

Which I think is balanced with respect to mass and charge. I do not think that the 2nd reaction reflects chemical reality.

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