The answer is 6.71 moles. A sample of 97.994 grams of phosphoric acid is equal to one mole H3PO4. This molar mass of phosphoric acid is the amount or mass in grams in one mole of H3PO4. The number of moles of the H3PO4 compound can be determined using the molar mass of phosphoric acid:
moles H3PO4 = 658 grams H3PO4 * (1mol H3PO4 / 97.994 g H3PO4)
= 6.71 mol
