On whether phosphoric acid is a strong acid
Taste all life on the strength of acid, phosphoric acid is one of them. Either phosphoric acid is a strong acid, or not. Now study its rationale to clarify its properties.

Strong acids dissociate completely in water, hydrogen ions come out smoothly, and their dissociation constants are large. View phosphoric acid, the molecular formula is\ (H_ {3} PO_ {3}\), in its structure, although there is trihydrogen, the hydrogen connected to phosphorus is difficult to dissociate, and only the dihydrogen connected to the hydroxyl group can be dissociated. The first-order dissociation constant\ (K_ {a1}\) is about\ (3.7\ times10 ^ {-2}\), and the second-order dissociation constant\ (K_ {a2}\) is about\ (2.9\ times10 ^ {-7}\).

Compared with strong acids, hydrochloric acid, sulfuric acid and other strong acids have very large dissociation constants and are almost completely dissociated in water. In contrast, phosphoric acid has a small dissociation constant and only partially dissociates in water, and the release of hydrogen ions is not complete.

Experiments were also tested to measure its conductivity with phosphoric acid solutions, which are weaker than strong acid solutions. The conductivity of the cover solution is related to the ion concentration. If the ion concentration is high, the conductivity is strong. The ion concentration of the phosphite solution is inferior to that of the strong acid, so the conductivity is weak. This also proves that it is not completely dissociated, and it is not a strong acid.

From the perspective, phosphite is not a strong acid. It decomposes in the middle of water, and the dissociation constant is limited, and the experimental evidence is also clear. The strength of the acid, when you study its essence, and observe its dissociation state, you can get the truth.