What mass of sodium hydroxide is required to react with 68.6 g of phosphoric acid to form a medium salt?

1. Let’s write down the reaction equation:

3NaOH + H3PO4 = Na3PO4 + 3H2O.

2. Find the amount of phosphoric acid:

n (H3PO4) = m (H3PO4) / M (H3PO4) = 68.6 g / 98 g / mol = 0.7 mol.

3. Using the reaction equation, we find the amount of sodium hydroxide, and then its mass:

3n (NaOH) = n (H3PO4)

n (NaOH) = n (H3PO4) / 3 = 0.7 mol / 3 = 0.23 mol.

m (NaOH) = n (NaOH) * M (NaOH) = 0.23 mol * 40 g / mol = 9.33 g.

Answer: m (NaOH) = 9.33 g.