The lab adds sodium hydroxide from a burette to a stirred hydrochloric acid vessel. As the volume increases, excess hydronium is neutralized and the pH rises slowly and then sharply through the equivalence point. A magnified view shows the residual ions.
• A graduated NaOH burette, a stirred HCl vessel, a pH electrode and meter and a magnified residual-ion view. • Sliders for HCl concentration, NaOH concentration (both 0.01 to 0.2 mol/L) and NaOH added (0 to 50 mL), with toggles for an automatic titration sweep and explanatory particles. • Readouts: pH, pOH, hydronium concentration, hydroxide concentration, volume added and equivalence volume. • Experiments: at equivalence pH is 7 with equal 10⁻⁷ M hydronium and hydroxide; the automatic sweep shows a sharp pH rise near 25 mL and stops at 50 mL.
H₃O⁺ + OH⁻ → 2 H₂O. The excess concentration is C_excess = (C_aV_a − C_bV_b)/(V_a + V_b), with [H⁺] − [OH⁻] = C_excess and [H⁺][OH⁻] = 10⁻¹⁴. Then pH = −log₁₀[H⁺] and V_eq = C_aV_a/C_b.
The model covers a strong monoprotic acid and a strong base with complete dissociation, additive volumes and ideal activities at 25°C. Water autoionization is included at equivalence. There is no weak-acid buffer model, and solution colors are a teaching overlay, not actual HCl or NaOH color.
The volume where moles of base equal moles of acid. In this lab V_eq = C_aV_a/C_b, and for equal 0.1 mol/L concentrations and 25 mL of acid it is at 25 mL with pH 7.
Hydronium concentration spans many powers of ten over a small volume range, so the logarithmic pH jumps quickly as the last excess acid is neutralized.
No. Only strong acid with strong base is modeled. Weak acids add buffering and a different equivalence pH, which this lab does not include.
Because water autoionizes with [H⁺][OH⁻] = 10⁻¹⁴ at 25°C, and when no excess acid or base remains the two are equal.