Titration Technique

Why this skill matters

Titration is the highest-mark practical skill on 0620. It appears on Paper 5 (planning), Paper 6 (alternative-to-practical with data processing), and as the basis for calculation questions on Papers 2-4. A single titration question can carry 6-10 marks. Understanding the procedure, apparatus, and error analysis is essential.

Method and technique

Setup

1. Rinse the burette with the solution it will contain (usually the acid). This avoids dilution. Then fill the burette to near the 0.00 cm3 mark using a funnel. Remove the funnel before reading.
2. Rinse the pipette with the solution it will contain (usually the alkali). Use a pipette filler to draw up the solution to above the 25.0 cm3 mark, then release slowly until the meniscus sits on the mark.
3. Transfer the pipetted solution into a clean conical flask.
4. Add 2-3 drops of indicator (not more, as excess indicator requires acid/alkali to change colour and introduces error).

Performing the titration

1. Record the initial burette reading to the nearest 0.05 cm3 (e.g., 0.50 cm3).
2. Open the burette tap and add the solution steadily while swirling the flask.
3. As the colour begins to change and then reverts on swirling, slow down. Near the end point, add half-drops by partially opening the tap and washing the drop in with distilled water from a wash bottle.
4. The end point is reached when one half-drop causes a permanent colour change that does not revert on swirling.
5. Record the final burette reading.
6. Calculate the titre: final reading minus initial reading.

Repeating for concordant results

1. The first titration is a rough titre: it tells you approximately where the end point is.
2. Repeat the titration. In the repeat, add the solution quickly to within 2 cm3 of the rough titre, then add dropwise.
3. Continue repeating until you have at least two concordant results (within 0.10 cm3 of each other).
4. Average the concordant values to obtain the mean titre.

Indicator choice

Indicator	Acid colour	Alkali colour	Use
Methyl orange	Red	Yellow	Strong acid + strong/weak alkali
Phenolphthalein	Colourless	Pink	Strong/weak acid + strong alkali

Universal indicator is not suitable because it changes colour gradually across a pH range. You cannot identify a precise end point with it.

Common errors and how to avoid them

Using universal indicator: This is the most frequently penalised error. Universal indicator is for approximate pH measurement, not titration.

Not rinsing apparatus with the correct solution: Rinsing the burette with water dilutes the acid. Rinsing the conical flask with the alkali adds extra alkali. The conical flask should be rinsed with water only (extra water does not change the moles of alkali present).

Overshooting the end point: Adding too much solution past the colour change. The solution is to approach the end point with half-drops.

Recording burette readings to 1 decimal place: Burette readings should be to 2 decimal places (nearest 0.05 cm3). Writing 23.5 instead of 23.50 loses precision marks on Paper 6.

Including the rough titre in the average: The rough titre is approximate and should be excluded when calculating the mean.

Marking points examiners look for

• Rinse burette with acid, pipette with alkali, conical flask with distilled water
• Name a suitable indicator (not universal indicator)
• Add indicator: 2-3 drops only
• Swirl the flask during addition
• End point: permanent colour change on addition of one half-drop
• Record readings to nearest 0.05 cm3
• Obtain concordant results (within 0.10 cm3)
• Calculate mean titre from concordant results only