Titration Lab Simulator – Acid-Base Curves Online

How titration works

Titration is a precise way to find the unknown concentration of an acid or base. You add a titrant of known concentration, drop by drop, to a fixed volume of the unknown analyte until the reaction is exactly complete — the equivalence point, where the moles of added titrant precisely match the moles of analyte. From the volume of titrant that took, you calculate the unknown concentration.

The shape of the pH curve as titrant is added tells the story. Far from equivalence the pH changes slowly; then it leaps almost vertically through the equivalence point; then it flattens again. This simulator plots that curve live as you add titrant, so the equivalence point appears as the steep midpoint of the jump.

Experiments to try in this simulation

1. Strong acid, strong base: titrate HCl with NaOH and watch a flat curve leap sharply through pH 7 at equivalence. The steepness of that jump is what makes the endpoint easy to detect.

2. Weak-acid buffering: titrate acetic acid with NaOH. Before equivalence the curve is gentle and flat — a buffer region — and its midpoint, the half-equivalence point, is where pH equals the acid's pKa.

3. Polyprotic acids: run a diprotic acid and find two separate equivalence points, one for each proton the acid gives up.

4. Choosing an indicator: pick phenolphthalein or methyl orange and check whether its colour change falls inside the steep part of the curve — the test of whether an indicator suits a given titration.

Key equations

At the equivalence point, moles of titrant equal moles of analyte: for a 1:1 reaction, M_acid·V_acid = M_base·V_base, which is how you solve for the unknown concentration. For a weak acid, the buffer region follows the Henderson-Hasselbalch equation, pH = pKa + log([A⁻]/[HA]); at the half-equivalence point the two species are equal, so pH = pKa — a quick way to read an acid's pKa straight off the curve.

The pH jumps so steeply at equivalence because, right at that point, a tiny further addition of titrant has almost nothing left to neutralize, so it swings the pH dramatically — which is exactly what makes indicators work.

Real-world applications

Titration is one of the most widely used techniques in real chemistry. Quality-control labs use it to measure the acidity of food and wine, the concentration of active ingredients in medicines, and the hardness or chlorine content of water. Environmental scientists titrate to monitor pollution and ocean acidification, and clinical labs use related methods for blood chemistry. The virtual workflow you practice here — choosing an indicator, reading an equivalence point, computing a concentration — is exactly what an analytical chemist does at the bench.