Acid-base titration simulator

A titration measures an unknown concentration by reacting it with a solution of known concentration. In this simulation you control the burette, adding sodium hydroxide to an acid sample while tracking pH. Learning goals: explain what the equivalence point is and how to find it on a titration curve; use $M_aV_a = M_bV_b$ to calculate an unknown concentration; describe why the pH jumps suddenly near equivalence.

Controls

• Titrant concentration: Sets the molarity of the base solution in the burette.
• Volume added: Adds base to the flask in fixed increments and updates the pH readout.
• Analyte selection: Chooses the acid sample in the flask (hydrochloric, nitric, or an unknown).
• Show curve / indicator: Toggles the titration curve plot and the color indicator in the flask.

The chemistry

Assumptions

• Only strong acid with strong base titrations are modeled.
• Solutions are dilute enough that concentration approximates activity.
• Temperature is fixed at 25°C, so the equivalence pH of a strong acid-strong base titration is 7.
• The indicator color change is assumed to occur at the equivalence point.

Guided activity

1. Add base in small increments and watch the pH readout after each addition.

2. Locate the steep vertical region of the curve and mark the equivalence point.

3. Repeat the titration with a weaker analyte and compare the curve shape.

4. Predict the equivalence volume with $M_aV_a = M_bV_b$ before running the simulation, then check your prediction.

Challenge questions

1. Find the unknown concentration of an acid sample to within 0.01 M using the fewest additions.

2. Explain why the curve is flat at the start, steep in the middle, and flat at the end.

3. Predict how the curve changes if you swap which solution is in the burette.