Calculate the Molar Mass of H3PO4

Q. Calculate the Molar Mass of H₃PO₄

The molar mass of H₃PO₄ is 98.00 g/mol. This means that there are 98 grams of H₃PO₄ in one mole of the substance. The molar mass measures the amount of matter in a given sample.

Characteristics of H₃PO₄

There are three hydrogen atoms and one phosphorus atom in each molecule of H₃PO₄. This gives the compound its name, derived from the Greek words for hydrogen (hydro) and phosphorus (Phos). The suffix “-ic” indicates that the compound is an acid.

H₃PO₄ is a strong acid dissociates completely in water to form H⁺ and PO₄³⁻ions. The H⁺ ions combine with water molecules to form hydronium ions (H₃O⁺), which are responsible for the acidic nature of the solution.

The PO43- ions combine with water molecules to form H₃PO₄. The presence of these ions gives H₃PO₄ its characteristic bitter taste.

In general, acids increase the concentration of H⁺ ions in a solution, while bases decrease the concentration of H⁺ ions. H₃PO₄ is classified as a diprotic acid because it can donate two protons (H⁺) per molecule.

Dissociation Steps

The first dissociation step is the ionisation of H₃PO₄, and the second is called the dissociation of HPO₄²⁻. The following equations represent these two steps:

H₃PO₄ + H₂O → H₃O+ + PO₄³⁻ (ionization)

HPO₄2- + H₂O → H₂PO₄⁻ + OH⁻ (dissociation)

The second dissociation step is much weaker than the first, which means most of the H3PO4 molecules will ionise before dissociating.

The Overall Reaction Can Be Simplified to:

H₃PO₄ + H₂O → 2H₃O+ + PO₄³⁻

This equation shows that one molecule of H₃PO₄ will yield two molecules of H₃O⁺ and one molecule of PO₄³⁻.

The H₃PO₄ molecule is held together by covalent bonds formed when atoms share electrons. However, the electrons are shared unequally, so the phosphorus atom has a partial negative charge and the hydrogen atoms have partial positive charges.