Question

Phosphoric acid$\left({\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}\right)$is a triprotic acid, phosphorous acid$\left({\text{H}}_{\text{3}}{\text{PO}}_3\right)$is a diprotic acid, and hypo phosphorous acid$\mathbf{\left(}{\mathbf{\text{H}}}_{\mathbf{\text{3}}}{\mathbf{\text{PO}}}_{\mathbf{2}}\mathbf{\right)}$is a monoprotic acid. Explain this phenomenon.

Short answer

Hydrogen attached to oxygen can be ionized. This is due to electronegativity differences between hydrogen and oxygen. Depending on number of such hydrogens, the acid is monoprotic, diprotic, or triprotic.

Step-by-step solution

Concept Introduction

Compounds are chemical compounds made up of two or more elements linked together chemically in a certain ratio.

Electronegativity is the tendency of an atom in a molecule to draw the shared pair of electrons towards itself

Chemical Structures

Phosphoric acid is a triprotic acid as it can donate three hydrogen ions.

Phosphorus acid is diprotic acid as it can donate two hydrogen ions even though it has three hydrogen atoms.

Hypo phosphorus acid is a monoprotic acid as it can donate one hydrogen ion even though it has three hydrogen atoms.

The structures of these acids are shown in the figure below.

Explanation for the Phenomena

Due to more electronegativity differences between hydrogen and oxygen, thehydrogen atom attached to oxygen is detached rather than the hydrogenattached to phosphorus.

When${\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}$is added to water,${\text{3H}}^{\text{+}}$ions are released because threeatoms are attached to oxygen. And that's why${\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}$is a triprotic acid.

Whenrole="math" localid="1663764836834" ${\text{H}}_{\text{3}}{\text{PO}}_3$is added to water, only${\text{2H}}^{\text{+}}$ions are released because twohydrogen atoms are attached to oxygen, and one hydrogen atom is attachedto phosphorus atom. That's why${\text{H}}_{\text{3}}{\text{PO}}_3$is a diprotic acid.

When${\text{H}}_{\text{3}}{\text{PO}}_2$is added to water, only${\text{1H}}^{\text{+}}$ion is released because only onehydrogen atom is attached to oxygen, and two hydrogen atoms are attachedto phosphorus. That's why${\text{H}}_{\text{3}}{\text{PO}}_2$is a monoprotic acid.

Therefore, the phenomenon is electronegativity difference.