QCE Chemistry - Unit 3 - Chemical equilibrium systems
Volumetric Analysis | QCE Chemistry
Learn titration calculations, aliquots, titres and stoichiometric reasoning for QCE Chemistry volumetric analysis.
Updated 2026-05-18 - 4 min read
QCAA official coverage - Chemistry 2025 v1.3
Exact syllabus points covered
- Discriminate between the terms end point and equivalence point.
- Sketch the general shapes of conductometric and acid-base titration curves involving strong and weak acids and bases. (Titration of weak acids to weak bases is not required.)
- Interpret acid-base titration curves to determine the intercept with pH axis, equivalence point, buffer region and points where pKa = pH or pKb = pOH.
- Interpret conductometric titration curves to determine the intercept with conductivity axis, equivalence point and volume of titrant.
- Analyse volumetric data, including solubility, conductometric and acid-base titration curves, to determine moles, mass, volume and concentration.
- Analyse titration curves to calculate the concentration of a solution with reference to a standard solution.
Volumetric analysis uses accurately measured solution volumes to calculate an unknown concentration. In QCE Chemistry, this usually means titration: a solution of known concentration reacts with a measured volume of another solution until the endpoint is reached.
Key vocabulary
- Standard solution: a solution with accurately known concentration.
- Primary standard: a pure, stable solid that can be weighed accurately to make a standard solution.
- Aliquot: the measured volume transferred by pipette into the conical flask.
- Titrant: the solution delivered from the burette.
- Titre: the volume delivered from the burette.
- Concordant titres: titres close enough to be averaged reliably.
Original Sylligence diagram for titration curve.
Making a standard solution
A good primary standard should be:
- pure
- stable in air
- not strongly hygroscopic
- soluble in water
- known by an accurate formula
- reasonably safe to handle
Typical process:
- Accurately weigh the solid.
- Dissolve it in distilled water.
- Transfer all solution to a volumetric flask, rinsing the beaker and funnel.
- Make up to the calibration line.
- Stopper and invert several times to mix.
Taking titres
In a titration, you usually do a rough titre first, then repeat carefully until you have concordant titres. The rough titre helps you know when to slow down near the endpoint.
Read the burette at eye level from the bottom of the meniscus. Record values to the correct precision, commonly two decimal places for a burette marked every $0.10\ \mathrm{mL}$.
Calculation process
Use this structure every time:
- Write the balanced equation.
- Identify the known solution and calculate moles using $n = cV$.
- Use the mole ratio to find moles of the unknown.
- Calculate concentration using $c = \frac{n}{V}$.
- Apply any dilution factor if the original sample was diluted before titration.
Always convert $\mathrm{mL}$ to $\mathrm{L}$ before using $n = cV$.
Worked example
Dilution example
If $10.00\ \mathrm{mL}$ of an original acid sample is diluted to $250.0\ \mathrm{mL}$, then a $25.00\ \mathrm{mL}$ aliquot of the diluted solution is titrated. The titration tells you the concentration of the diluted solution. To get back to the original concentration, multiply by the dilution factor:
$ \frac{250.0}{10.00} = 25.00 $
So:
$ c(\text{original}) = 25.00 \times c(\text{diluted}) $
Exam traps
Other traps:
- using $\mathrm{mL}$ instead of $\mathrm{L}$ in $n = cV$
- ignoring the balanced equation ratio
- averaging non-concordant titres
- forgetting dilution factors
- overshooting the endpoint and treating the result as reliable