1. Write the Balanced Chemical Equation:

The reaction between potassium hydroxide (KOH) and phosphoric acid (H₃PO₄) is:

3KOH + H₃PO₄ → K₃PO₄ + 3H₂O

2. Determine the Mole Ratio:

The balanced equation shows that 3 moles of KOH are needed to neutralize 1 mole of H₃PO₄.

3. Calculate Moles of Phosphoric Acid:

You haven't provided the concentration of the phosphoric acid solution, so we'll assume you have 1.56 moles of pure H₃PO₄.

4. Calculate Moles of Potassium Hydroxide:

Using the mole ratio from step 2:

(1.56 moles H₃PO₄) * (3 moles KOH / 1 mole H₃PO₄) = 4.68 moles KOH

Therefore, 4.68 moles of potassium hydroxide are needed to completely neutralize 1.56 moles of phosphoric acid.