d. 0.0166 mol/L
Step 1. Write the balanced chemical equation
2H3PO4 + 3Ba(OH)2 → Ba3(PO4)2 + 6H2O
Step 2. Calculate the moles of Ba(OH)2
Moles of Ba(OH)2 = 876 mL Ba(OH)2 x [0.0102 mmol Ba(OH)2 /1 mL Ba(OH)2] = 8.935 mmol Ba(OH)2
Step 3. Calculate the moles of H3PO4
Moles of H3PO4 = 8.935 mmol Ba(OH)2 x (2 mmol H3PO4/3 mmol Ba(OH)2) = 5.957 mmol H3PO4
Step 4. Calculate the molar concentration of the H3PO4
c = moles/litres = 5.957 mmol /358 mL = 0.0166 mol/L