# A buffer solution is formed when 10.0 cm^3 of 0.230 mol dm^-3 aqueous sodium hydroxide are added to 30.0 cm^3 of 0.550 mol dm^-3 aqueous propanoic acid. How do you calculate the number of moles of propanoic acid originally present?

$0.030 \text{mL" * (0.550"mol")/"L" approx 1.65*10^-2"mol}$