Common Titration Errors and How to Avoid Them

A good titration can measure a concentration to better than 1%. A careless one can be out by 10% or more while still looking perfectly tidy on paper. The difference is almost always in small technique errors, each of which pushes the result in a predictable direction.

Knowing those directions is useful twice over: it helps you do better practical work, and it’s one of the most commonly examined skills in chemistry. For each error below, we say what happens to the titre (the volume from the burette) and to the calculated concentration of the unknown.

Throughout, assume the standard setup: a solution of known concentration in the burette, and a pipetted volume of the unknown in the conical flask. The unknown concentration is calculated as:

c(unknown) = (c(burette) × titre × ratio) ÷ volume pipetted

So a titre that’s too big gives a calculated concentration that’s too big, and vice versa. For the full method, see acid–base titration.

Errors with the burette

1. Burette rinsed with water but not with the titrant

The water left inside dilutes the titrant, so each cm³ contains fewer moles. You need more titrant to reach the end point.

• Titre: too high
• Calculated concentration of unknown: too high
• Fix: rinse the burette with a few cm³ of the titrant and drain it before filling.

2. Air bubble in the burette tip

If a bubble below the tap escapes during the titration, the burette reading changes by the volume of the bubble even though no liquid was delivered.

• Titre: too high (recorded volume bigger than liquid actually added)
• Calculated concentration: too high
• Fix: run some liquid through the tap after filling to clear the tip before taking the initial reading.

3. Funnel left in the burette

Drops from the funnel can fall in during the titration, making the burette reading lower than it should be at the end.

• Titre: usually too low, and unpredictable
• Fix: always remove the funnel before reading and titrating.

4. Reading the burette from above or below eye level (parallax)

Reading from above makes the meniscus appear lower down the scale than it really is; reading from below makes it appear higher. If you’re consistent, the errors partly cancel between initial and final readings, but inconsistency causes random errors.

• Fix: read at eye level, from the bottom of the meniscus, against a white card.

5. Leaking burette tap

Liquid drips out between readings without entering the flask.

• Titre: too high
• Fix: check for leaks before starting; grease or replace the tap.

6. Reading to the wrong precision

Burettes should be read to the nearest 0.05 cm³, and all readings recorded to two decimal places (ending in 0 or 5).

Errors with the pipette

7. Pipette rinsed with water but not with the solution

Water left inside dilutes the sample, so the 25.00 cm³ delivered contains fewer moles of the unknown.

• Titre: too low
• Calculated concentration: too low
• Fix: rinse the pipette with the solution it will measure.

8. Blowing out the last drop

Volumetric pipettes are calibrated to leave a small drop in the tip. Blowing it out delivers extra solution.

• Titre: too high (more moles of the unknown in the flask)
• Calculated concentration: too high (the calculation still assumes 25.00 cm³)
• Fix: let it drain naturally, then touch the tip to the inside of the flask.

9. Filling past the mark or reading the meniscus wrongly

Delivers the wrong volume. Filling above the mark gives too much sample and a high titre; stopping below it gives too little.

• Fix: the bottom of the meniscus should sit exactly on the line, at eye level.

Errors with the flask and indicator

10. Conical flask rinsed with the solution instead of water

Leftover solution in the flask adds extra moles to the pipetted sample.

• Titre: too high
• Calculated concentration: too high
• Fix: rinse the conical flask with distilled water only. Water left in the flask doesn’t matter, because it doesn’t change the number of moles you pipetted in.

11. Using the wrong indicator

If the indicator’s colour change range lies outside the steep part of the titration curve, the end point won’t match the equivalence point. For example, phenolphthalein in an ammonia–hydrochloric acid titration changes too early.

• Titre: too high or too low depending on the case, often by several cm³
• Fix: choose the indicator carefully. See how to choose an indicator.

12. Adding too much indicator

Indicators are weak acids and use up a tiny amount of titrant; strong colours are also harder to judge.

• Fix: two or three drops is enough.

Errors of technique at the end point

13. Overshooting the end point

Adding titrant too quickly near the end means a drop or more too much.

• Titre: too high
• Calculated concentration: too high
• Fix: do a rough titration first, then add dropwise within about 2 cm³ of the rough value. Use half-drops near the end.

14. Not swirling enough

Local excess of titrant can cause a temporary colour change before the solution is fully mixed, tempting you to stop early.

• Titre: too low if you stop early
• Fix: swirl constantly and wait a few seconds to check the colour is permanent.

15. Titrant splashes on the flask walls

Drops that stick to the inside wall haven’t reacted.

• Titre: effectively too high (volume recorded but not reacted)
• Fix: rinse the walls with a little distilled water from a wash bottle near the end point.

Errors in the solutions themselves

• Standard solution not accurately prepared (for example, a solid not fully dissolved, or not made up exactly to the mark in the volumetric flask). All results will be systematically off.
• Sodium hydroxide absorbing CO₂ from the air. NaOH solution slowly reacts with carbon dioxide, lowering its hydroxide concentration. Store it sealed, and standardise it against a primary standard before accurate work.
• Hygroscopic solids. Solids that absorb water from the air (like solid NaOH) can’t be weighed accurately to make standard solutions. Primary standards, such as potassium hydrogenphthalate or anhydrous sodium carbonate, are used instead.

Summary table

Error	Titre	Calculated concentration of unknown
Burette not rinsed with titrant	↑	↑
Air bubble escapes from burette tip	↑	↑
Pipette not rinsed with sample	↓	↓
Last drop blown out of pipette	↑	↑
Flask rinsed with sample solution	↑	↑
Water left in flask	no change	no change
Overshooting end point	↑	↑
Stopping at a temporary colour change	↓	↓

Random vs systematic errors

• Systematic errors push every result the same way (for example, an unrinsed burette). Repeating the titration doesn’t remove them; the titres may still be concordant but wrong.
• Random errors vary from titration to titration (for example, judging the exact colour). Repeating and averaging concordant titres reduces them.

This is why concordant results show good precision (close agreement with each other), but not necessarily good accuracy (closeness to the true value).

Key takeaways

• Rinse the burette and pipette with their own solutions; rinse the flask with water.
• Clear air bubbles, remove the funnel and read the meniscus at eye level.
• Don’t blow out the pipette’s last drop, and add titrant dropwise near the end point.
• Most errors make the titre too high, which makes the calculated concentration of the unknown too high.
• Concordant results show precision; avoiding systematic errors gives accuracy.
• Practise the calculations in titration calculations.