Determine the equivalent mass of phosphoric acid in the reaction: H3PO4 + 2NaOH = Na2HPO4 + 2H2O

| April 6, 2021 | education

Reaction equation
H3PO4 + 2NaOH = Na2HPO4 + 2H2O
Sodium hydroxide equivalence factor
feq (NaOH) = 1 / x (OH) = 1 / z (Na) = 1, where
x (OH) = 1 is the number of hydroxyl groups in NaOH
z (Na) = 1 – sodium valence
According to the reaction equation
n (H3PO4) / n (NaOH) = 1/2
Let’s use the law of equivalents in the following formulation:
Substances react with each other in quantities proportional to their chemical equivalents. And since the equivalence factor is numerically equal to the chemical equivalent, then this law of equivalents can be rewritten as
n (NaOH) / n (H3PO4) = feq (NaOH) / feq (H3PO4)
Hence the equivalence factor of phosphoric acid in this reaction
feq (H3PO4) = feq (NaOH) * n (H3PO4) / n (NaOH) = 1 * (1/2) = 1/2
Then the molar mass of the equivalent of phosphoric acid for this reaction
Meq (H3PO4) = feq (H3PO4) * M (H3PO4) = 98/2 = 49 g / mol



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