# Reaction of sulphuric acid with ammonium hydrogen phosphate [closed]

How will the reaction of $$\ce{H2SO4}$$ with ($$\ce{NH4)2HPO4}$$ [diammonium phosphate, commonly used DAP fertiliser in agriculture] proceed? Will phosphoric acid be produced, or a complex phosphate-sulphate salt would be the result?

Depending on the molar ratio,

$$\ce{HPO4^2- ->[H+]H2PO4- ->[H+]H3PO4}.$$

Also remember there are no $$\ce{H2SO4}$$ nor $$\ce{(NH4)2HPO4}$$ in water solution, but $$\ce{,}$$ $$\ce{HSO4-(aq)}$$, $$\ce{SO4^2-(aq)}$$ , $$\ce{NH4+(aq)}$$ , $$\ce{HPO4^2-(aq)}$$, $$\ce{H2PO4^-(aq)}$$ and $$\ce{H3PO4(aq)}$$, depending on the ratio and $$\mathrm{pH}$$.

For direct reaction without water, then

$$\ce{2 H2SO4 + (NH4)2HPO4 -> 2 NH4HSO4 + H3PO4},$$

with some $$\ce{(NH4)2SO4}$$ too.

• Thank you, that’s very helpful :). From your explanation, I conclude that if the objective is to get P04 3- (soluble form of phosphate ion in acidic PH for the crop) from DAP, then a higher concentration of H2S04 should be used than an equal moles of both, and the reaction should be carried out in water. Nov 18, 2022 at 22:26
• PO4^3- is present only at very alkalic solutions. (pK_a3= 12.37) Nov 19, 2022 at 0:43