Question #5650b

1 Answer
Sep 17, 2015

Sodium forms three anhydrous monophosphates with the three phosphates.

Explanation:

Sodium and the phosphate anion can actually only form one compound, trisodium phosphate, "Na"_3"PO"_4.

The other two compounds you're probably referring to are actually formed with the dihydrogen phosphate, "H"_2"PO"_4^(-), and hydrogen phosphate, "HPO"_4^(2-), anions.

Moreover, sodium can form monophosphates and polyphosphates, in several anhydrous and hydrate forms, so I will assume that you're interested in the anhydrous monophosphates here.

  • monosodium phosphate

This compound is formed when one sodium cation, "Na"^(+), combines with one dihydrogen phosphate anion, "H"_2"PO"_4^(-).

The salt dissociates completely in aqueous solution

"NaH"_2"PO"_text(4(aq]) -> "Na"_text((aq])^(+) + "H"_2"PO"_text(4(aq])^(-)

  • disodium phosphate

This compound is formed when two sodium cations combine with one hydrogen phosphate anion, "HPO"_4^(2-).

"Na"_2"HPO"_text(4(aq]) -> 2"Na"_text((aq])^(+) + "HPO"_text(4(aq])^(2-)

  • trisodium phosphate

This time, you have three sodium cations and one phosphate anion, "PO"_4^(3-).

"Na"_3"PO"_text(4(aq]) -> 3"Na"_text((aq])^(+) + "PO"_text(4(aq])^(3-)