If I spill 100ml of a .5 M H3PO4 solution, how many grams of NaOH should be dissolved in water and added to the spill to neutralize the acid?

Answer 1

H3PO4 + 3NaOH ==> Na3PO4 + 3H2O
mols H3PO4 = M x L = ?
mols NaOH = 3x that.
mols NaOH = grams/molar mass. You know mols and molar mass, solve for grams.