To calculate the mass of 4.76 moles of Na3PO4, you need to know the molar mass of Na3PO4. The molar mass of a compound is the sum of the atomic masses of all the atoms in the compound. For Na3PO4, the molar mass is:

3 × (22.99 g/mol) + 1 × (30.97 g/mol) + 4 × (16.00 g/mol) = 163.94 g/mol

Therefore, the mass of 4.76 moles of Na3PO4 is:

4.76 mol × 163.94 g/mol = 780.8 g