How many grams of sodium hydroxide is required to neutralize a solution containing 9.8 grams of phosphoric acid.

Given:
m (H3PO4) = 9.8 g

To find:
m (NaOH) -?

Solution:
1) H3PO4 + 3NaOH => Na3PO4 + 3H2O;
2) M (H3PO4) = Mr (H3PO4) = Ar (H) * N (H) + Ar (P) * N (P) + Ar (O) * N (O) = 1 * 3 + 31 * 1 + 16 * 4 = 98 g / mol;
3) n (H3PO4) = m (H3PO4) / M (H3PO4) = 9.8 / 98 = 0.1 mol;
4) n (NaOH) = n (H3PO4) * 3 = 0.1 * 3 = 0.3 mol;
5) M (NaOH) = Mr (NaOH) = Ar (Na) * N (Na) + Ar (O) * N (O) + Ar (H) * N (H) = 23 * 1 + 16 * 1 + 1 * 1 = 40 g / mol;
6) m (NaOH) = n (NaOH) * M (NaOH) = 0.3 * 40 = 12 g.

Answer: The mass of NaOH is 12 g.