How does #H_3PO_4# behave as an acid?

Question

Noah Aldrich · Accepted Answer

You have not quoted #K_a# values for #H_3PO_4# or #H_2PO_4^(-)#.......

As per the findings, phosphoric acid exhibits speciation in solution. #H_3PO_4(aq) + H_2O(l) stackrel(K_(a1))rightleftharpoonsH_2PO_4^(-)(aq) + H_3O^(+)# Additionally. #H_2PO_4^(-)(aq) + H_2Ostackrel(K_(a2))rightleftharpoonsHPO_4^(2-)(aq) + H_3O^(+)# We need #K_(a1)# and #K_(a2)# before we can address your question.

Natalie Anton · Answer

undefined H3PO4 behaves as an acid by donating one, two, or three protons (H+) in aqueous solutions, depending on the pH of the solution and the reaction conditions. It can undergo sequential ionization reactions to form H2PO4-, HPO4^2-, and PO4^3- ions, known as dihydrogen phosphate, hydrogen phosphate, and phosphate ions, respectively.

Cooper Adams · Answer

undefined H₃PO₄, or phosphoric acid, behaves as a triprotic acid, meaning it can donate three protons (H⁺ ions) successively. In aqueous solution, it undergoes stepwise dissociation reactions:

1. The first dissociation:
$$ \text{H₃PO₄} \rightleftharpoons \text{H⁺} + \text{H₂PO₄⁻} $$
This reaction yields one hydrogen ion (H⁺) and the dihydrogen phosphate ion (H₂PO₄⁻).

2. The second dissociation:
$$ \text{H₂PO₄⁻} \rightleftharpoons \text{H⁺} + \text{HPO₄²⁻} $$
This reaction yields another hydrogen ion (H⁺) and the hydrogen phosphate ion (HPO₄²⁻).

3. The third dissociation:
$$ \text{HPO₄²⁻} \rightleftharpoons \text{H⁺} + \text{PO₄³⁻} $$
This reaction yields the third hydrogen ion (H⁺) and the phosphate ion (PO₄³⁻).

In each dissociation step, H₃PO₄ donates one proton, resulting in the formation of a conjugate base. Phosphoric acid is considered a weak acid, meaning it only partially dissociates in water, and the equilibrium lies to the left, favoring the undissociated acid form. However, because it is a triprotic acid, it can release multiple hydrogen ions in solution, making it versatile for various acid-base reactions.