Two phosphoric acid molecules can combine to make pyrophosphoric acid and another molecule as shown here. The pyrophosphoric acid molecule is a phosphoester and is a structural element in the ADP/ATP metabolic energy system. What molecule is represented by the question mark in the structural reaction equation below?

Question

Quizplus · Accepted Answer

The structural formula for pyrophosphoric acid is HS1U1P2S1U1P2S1U1OH. When two phosphoric acid molecules combine, they lose a water molecule and form a phosphoanhydride bond between the two phosphate groups, resulting in the formation of pyrophosphoric acid (HS1U1P2S1U1P2S1U1OH) and a molecule containing a phosphate group. The only answer choice with a phosphate group is C, which represents the molecule H2PO4-.

Two Phosphoric Acid Molecules Can Combine to Make Pyrophosphoric Acid