Na2H(PO4)+NaH2(PO4)+HCl =?

Answer 1

This really depends upon the quantity of and concentration of the HCl solution.

Dibasic and Monobasic Hydrogen Phosphate and usually used in a buffering system. Small amounts of HCl would shift the relative amounts of the Dibasic and Monobasic salts forming a little Sodium Chloride.

A large excess of HCl would complete the following reaction:

Na2H(PO4) + NaH2(PO4) + 3HCl = 3NaCl + H3PO4

in any case, all of the ions would remain in solution.

Answer 2

Depends on the amount of HCl added. If you're only adding one equivalent to equal amounts of Na2HPO4 and NaH2PO4, you will convert all of the hydrogen phosphate into the dihydrogen phosphate. If you add more equivalents, you will start converting dihydrogen phosphate into phosphoric acid.

Answer 3

It depends