# How many hydrogen atoms in phosphate salts?

Suppose we have the following chemical formula, say ammonium dihydrogenphosphate $\left(N {H}_{4}\right) \left({H}_{2} P {O}_{4}\right)$. This is the ammonium salt of phosphoric acid, ${H}_{3} P {O}_{4}$. Its elemental composition is $N {H}_{6} P {O}_{4}$, and here I have simply added the elements; but such a composition makes little chemical sense in that it is not immediately obvious that it is the ammonium salt of phosphoric acid, as the first formulation does.
Alternatively, I could have a transition metal complex, say $\left[C o {\left(M {e}_{2} N C {H}_{2} C {H}_{2} N M {e}_{2}\right)}_{2} C {l}_{2}\right] C l$. If I made this and sent it off for combustion analysis I would present it as $C o C {l}_{3} {C}_{12} {H}_{32} {N}_{4}$. After combustion, the carbon would come off as $C {O}_{2}$, the hydrogens as ${H}_{2} O$, and the nitrogens as ${N}_{2}$, and I would get a very accurate determination of the purity of my compound. A Mohr tritration would give halogen content.