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Premium experiment • stoichiometry meets equilibrium

CHEMISTRY • ACIDS & BASES

Acid,Base Titration

Compare strong- and weak-acid titrations with a strong base. Follow the live pH curve through the buffer region, half-equivalence, equivalence and excess-base regions.

● TITRATION CURVEAcid,Base Titration
Current pH
Equivalence volume
Region
Total volume

Reasoning inspector

live model state
Analyte mode—
pH—
Equivalence volume—
% of equivalence—
Current region—
Acid moles—
Base moles added—
Total volume—

Explore the whole titration curve

Equivalence is set by mole balance, not by a universal pH. Weak acids form a buffer before equivalence and a basic conjugate-base solution at equivalence.

LEARN WITH THE SIMULATION

Understand Acid,Base Titration by experimenting.

START HERE

An acid,base titration passes through chemically different regions rather than following one pH formula from start to finish. This laboratory compares strong-acid and weak-acid analytes titrated with strong base. It tracks acid and base moles, equivalence volume, fraction of equivalence, current region and pH while plotting the full curve. The premium challenge highlights half-equivalence and equivalence as reasoning landmarks.

BUILD THE IDEA

What you should understand first

  • Calculate equivalence volume from stoichiometric mole balance.
  • Identify weak-acid, buffer, near-equivalence, equivalence and excess-base regions.
  • Explain why pH≈pKa at half-equivalence for a weak acid.
  • Explain why weak-acid/strong-base equivalence is basic while strong-acid/strong-base equivalence is near neutral in the ideal model.

TRY IT YOURSELF

Why does the same added-base fraction require different pH reasoning before, at and after equivalence?

  1. Use weak-acid mode and move base volume to about 50% of equivalence; compare pH with pKa.
  2. Move to equivalence and record pH and remaining acid/base mole balance.
  3. Move beyond equivalence and observe how excess strong base controls pH.
  4. Switch to strong-acid mode with the same stoichiometric setup and compare the equivalence-point pH.
Read the visual:

Different species dominate in different regions. The weak-acid buffer uses the acid/conjugate-base ratio before equivalence, conjugate-base hydrolysis matters at equivalence, and excess hydroxide controls pH after equivalence. Strong-acid equivalence lacks the weak conjugate-base effect.

WHY IT WORKS 01

Equivalence volume is fixed by moles, not by the shape of the pH curve

For a monoprotic acid titrated 1:1 with strong base, equivalence occurs when added base moles equal initial acid moles. Thus Veq = CaVa/Cb. Changing acid or base concentration moves the equivalence volume even before any equilibrium pH calculation is performed.

WHY IT WORKS 02

Half-equivalence exposes the Henderson,Hasselbalch structure

Before equivalence in a weak-acid titration, added base converts part of HA into A⁻. At half-equivalence their amounts are equal, so log([A⁻]/[HA])=0 and the Henderson,Hasselbalch equation gives pH=pKa. This landmark is a direct way to infer pKa experimentally from an ideal titration curve.

WHY IT WORKS 03

The equivalence-point chemistry depends on the conjugate species

A strong acid neutralized by strong base leaves an ideal neutral salt and water, so equivalence is near pH 7 at 25°C. A weak acid leaves its conjugate base at equivalence; that base hydrolyzes water and creates OH⁻, making the equivalence solution basic. Beyond equivalence, excess added strong base dominates both cases.

DO NOT MIX THESE UP

Common misconception

Equivalence is defined by stoichiometric mole balance, not by pH=7 in every titration. Half-equivalence is not half the final pH; for a weak acid it is the point where acid and conjugate base are equal, giving pH≈pKa. An indicator endpoint is an experimental observation near equivalence, not the exact theoretical definition.

PRACTICE CHALLENGE

Can you navigate to half-equivalence and equivalence and explain which chemical model controls pH at each landmark?

  • In weak-acid mode, move base added to approximately 50% of equivalence and verify pH≈pKa.
  • Move to 100% of equivalence and explain why the weak-acid pH is above 7.
  • Switch to strong-acid mode while preserving stoichiometric concentrations and compare equivalence pH.
  • Move beyond equivalence and explain why the analyte type matters less once excess strong base dominates.
Reveal the reasoning

Half-equivalence of a weak acid has equal HA and A⁻, so pH≈pKa. At equivalence all initial weak acid has become conjugate base, whose hydrolysis makes the solution basic. Strong-acid/strong-base equivalence is approximately neutral in the ideal model, and after equivalence the excess OH⁻ from titrant sets pH.

MODEL BOUNDARIES

What this simulation assumes

Every simulation simplifies reality or a mathematical system. These are the assumptions and limits to keep in mind while interpreting the results.

Model assumptions

  • The titrant is a strong monoprotic base and the analyte is either a strong monoprotic acid or a weak monoprotic acid.
  • Volumes are additive, temperature is treated as fixed and the water ion product is approximated by Kw = 1×10⁻¹⁴.
  • Weak-acid buffer pH uses the Henderson,Hasselbalch relationship away from the initial and equivalence special cases.

Model limitations

  • Activity coefficients, polyprotic equilibria, dilution-dependent pKa, indicator chemistry and ionic-strength corrections are not represented.
  • Very concentrated or extremely dilute solutions can depart from ideal concentration-based pH calculations used in this educational model.

CONNECT IT

Where this matters

  • Analytical concentration measurement
  • Acid/base standardization
  • Buffer and formulation chemistry
  • Water, food and pharmaceutical analysis

WORDS THAT MATTER

Key vocabulary

Equivalence point
Stoichiometric point where titrant moles have reacted with analyte in the balanced ratio.
Half-equivalence
Weak-acid titration point where half the acid has been converted to conjugate base and pH≈pKa.
Buffer region
Pre-equivalence region containing appreciable weak acid and conjugate base.
Conjugate-base hydrolysis
Reaction of the weak acid's conjugate base with water that raises pH at equivalence.
Titration curve
Plot of pH against added titrant volume.