Neutralization and titration
An acid and a base react to form water and a salt, which is an ionic compound. This is neutralization.
acid + base → salt + water
HCl + NaOH → NaCl + H2O
The H+ from the acid and the OH− from the base combine into H2O. The leftover ions make up the salt.
A titration finds an unknown concentration. A solution of known concentration is added slowly to the unknown until the acid and base have exactly reacted. An indicator changes color at that point, called the endpoint.
At the endpoint, moles of H+ equal moles of OH−. For an acid and base that react 1 to 1:
Ma × Va = Mb × Vb
Worked example: a titration
25.0 mL of HCl is neutralized by 20.0 mL of 0.500 M NaOH. What is the concentration of the acid?
Ma × 25.0 mL = 0.500 M × 20.0 mL
Ma = 10.0 M·mL ÷ 25.0 mL = 0.400 M
Common mistake
Using the 1 to 1 formula when the ratio is different. H2SO4 releases two H+ per formula unit, so 1 mol of it neutralizes 2 mol of NaOH. Write the balanced equation and use its mole ratio.