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TL;DR The burette is graduated 0 to 50 cm³ from top to bottom -- the scale runs downward because you are measuring how much you have dispensed, not how much remains. Two accurate titrations are concordant when their titres differ by no more than 0.10 cm³; use only these concordant values to calculate your mean. Never average the rough titration with the accurate runs; it will push your mean up and lose you marks.
This post covers the Sec 3 entry point for how to use a burette in a titration, with a worked example of the concordant-results rule and step-by-step titration table construction. For broader O-Level coverage -- stopcock technique, hand positioning, the half-turn method, and how burette marks are scored in Paper 3 -- read our companion guide on how to use a burette correctly for O-Level Chemistry titration. For meniscus-reading technique applied to measuring cylinders, see our how to read a measuring cylinder guide. For the full titration workflow -- planning, indicators, ACE write-ups, and practice loops -- see the O-Level Chemistry Titration Playbook.
1 | Parts of a burette
A burette is a long, narrow glass tube with a stopcock (tap) at the bottom. The standard school burette holds 50 cm³.
The four key parts to know by name:
Opening (top): where you fill the burette using a funnel. The funnel is removed before the titration begins.
Barrel: the long graduated tube. The graduation marks run from 0.00 cm³ at the top to 50.00 cm³ at the bottom. This is the most important feature to memorise: the scale runs down because the burette measures how much solution you have delivered, not how much remains in the tube.
Stopcock: the glass or plastic tap that controls the flow of liquid out of the barrel. One quarter-turn opens it; another quarter-turn closes it. Learning to control flow with a half-turn is a key practical skill for the accurate titration runs.
Tip (jet): the narrow glass tube below the stopcock where the solution exits into the conical flask. Air bubbles can become trapped here after filling and must be expelled before any reading is taken.
Why does the scale run downward? Because when you deliver solution from the burette, the liquid level drops. A falling liquid level on a scale that increases downward means your delivered volume (final reading minus initial reading) is always a positive number. This direction is the opposite of a measuring cylinder and catches many students out in their first few titrations.
This is the step most students rush. Rushing here is the single largest source of systematic error in Sec 3 titrations. Follow the sequence below every time.
Step 1: Rinse the burette twice with the titrant, not with water.
Pour a small volume of the solution the burette will contain -- usually the acid -- into the burette. Tilt and rotate the burette to wet the entire inner surface, then drain through the tip into a waste beaker. Repeat once more.
Rinsing with distilled water instead of the titrant is a classic error. Any water left inside the burette dilutes your titrant and lowers its effective concentration. Your titres will come out larger than the true value -- a systematic positive error that repeats across every run.
Step 2: Fill above the zero mark.
Use a funnel to pour titrant into the burette until the meniscus sits a few centimetres above the 0.00 cm³ mark. Remove the funnel before you begin -- a funnel left in the burette can drip, adding untracked volume to your titre.
Step 3: Expel the air bubble from the tip.
Open the stopcock fully and let solution rush through the tip into a waste beaker for two to three seconds. Watch the jet: any trapped air bubble will be swept out by the fast flow. A bubble that remains and dislodges mid-titration adds phantom volume that was never actually delivered to the flask. The titre will appear lower than the true value.
Step 4: Check the tip at eye level.
Bend until your eyes are level with the tip. Confirm there is no air bubble trapped at the base of the stopcock or inside the narrow jet.
Step 5: Adjust to the initial reading.
Lower the liquid level to just at or below 0.00 cm³ using the stopcock, then record the exact initial reading using the meniscus technique in Section 4. Write this value into your results table immediately.
3 | Rough titration versus accurate titrations
Every titration sequence in O-Level Chemistry Paper 3 follows the same two-phase structure: one rough run followed by two or more accurate runs. Understanding why both phases exist is what distinguishes a student who gets method marks from one who does not.
The rough titration
Open the stopcock to a steady stream and add solution at full flow. Swirl the conical flask continuously. Watch the indicator: as you approach the endpoint, a transient colour change will appear and disappear as you swirl. When the colour change becomes permanent on the next drop, stop immediately and record the final reading. Calculate the rough titre.
The rough titration gives you the approximate endpoint. You are not trying to nail it precisely here -- you are locating it within about 0.5 cm³ so you know where to slow down in the accurate runs. Label this row "Rough" in your table and never use it in the mean.
The accurate titrations
Refill the burette to near 0.00 cm³ and record the new initial reading. Add solution at moderate flow until you are about 1 to 2 cm³ below the rough titre. Then switch to dropwise addition, swirling after each drop. In the final 0.5 cm³, add half-drops by opening the stopcock just enough for a partial drop to form on the tip, then rinsing it into the flask with a small jet of distilled water from the wash bottle.
Stop the moment the indicator shows a permanent colour change. Record the final reading. Calculate the titre.
Repeat the accurate run until you have two concordant titres. The concordant rule is explained in Section 5.
4 | Reading to 0.05 cm³
Every burette reading in O-Level Chemistry must be recorded to the nearest 0.05 cm³. This precision requirement follows directly from the scale of the instrument.
The graduation interval is 0.10 cm³. Each etched line on the barrel represents a 0.10 cm³ step. You must estimate whether the bottom of the meniscus falls on a line or halfway between two lines. That half-interval estimate is 0.05 cm³.
Read the bottom of the meniscus for aqueous solutions. For colourless or lightly coloured solutions, the liquid surface curves upward at the edges where it meets the glass, forming a concave meniscus. Read the scale at the lowest point of that curve -- not at the edges.
Your eyes must be level with the meniscus. If you look down at the meniscus, refraction makes it appear lower than it actually is (you record a volume that is too small). If you look up, the reverse happens. This optical distortion is called parallax error. In practice, this means bending your knees or adjusting the retort stand height, not tilting the burette.
Recording the reading correctly:
Every valid burette reading ends in either 0 or 5 in the hundredths place. The complete set of valid hundredths digits is:
.00, .05, .10, .15, .20, .25, .30, .35, .40, .45, .50, ... (and so on, up to .95).
If the meniscus bottom is halfway between the 23.50 cm³ and 23.60 cm³ lines, record 23.55 cm³. Do not round to 23.5 or 23.6. The two-decimal-place format with the last digit being 0 or 5 tells the examiner you have read the instrument correctly. A reading of 23.52 implies you can resolve 0.01 cm³ from a burette, which is impossible -- that reading will cost you marks.
5 | The concordant-results rule (within 0.10 cm³)
Two titration results are concordant when their titres differ by no more than 0.10 cm³. This is the threshold used in most O-Level mark schemes and in the SEAB 6092 practical paper.
Worked example:
Suppose you obtain the following titres from three runs:
The 2nd accurate titre (25.10 cm³) is discarded. The concordant pair is 24.40 and 24.45 cm³. The mean titre is:
Mean titre = (24.40 + 24.45) / 2 = 24.425, which is recorded as 24.43 cm³.
The mean is quoted to 2 decimal places.
Why you must never average the rough with the accurate values:
The rough titration is an intentional overshoot. By definition, you do not slow to dropwise addition before the endpoint -- you blow through it at full flow. The titre is almost always a few tenths of a cm³ too large. Including it in the mean inflates your calculated titre and produces an incorrect concentration in the ACE calculation section. Mark schemes explicitly state the rough result is excluded from the mean.
6 | Building the titration table
The titration table is where your PDO (Presenting Data and Observations) marks are earned or lost. A correctly structured table signals to the examiner that you understand the experiment design, not just the mechanics of operating the burette.
The required columns are:
Titration
Final reading / cm³
Initial reading / cm³
Titre / cm³
Use for mean?
Rough
25.50
0.00
25.50
No
1st accurate
24.40
0.00
24.40
Yes
2nd accurate
25.10
0.00
25.10
No
3rd accurate
24.45
0.00
24.45
Yes
Mean titre (from concordant 1st and 3rd accurate): 24.43 cm³
Rules for a full-mark table:
Include all runs -- rough plus every accurate titration, even the one you reject. Omitting a discarded titre suggests you fabricated the concordance.
Show both initial and final readings separately, never just the titre. Examiners check that Final minus Initial equals the stated titre.
Record every reading to two decimal places ending in 0 or 5.
Label the "Use for mean?" column explicitly. Writing "No" for the rough and for any non-concordant accurate runs shows you understand the selection rule.
Quote the mean to 2 decimal places. If the raw average is 24.425, round to 24.43 cm³. Do not write 24.4 or 24.425 in your final answer.
State clearly which rows are concordant -- either in the "Use for mean?" column or in a note below the table.
If you only ran one accurate titration before the time ran out, record it and note that a second concordant run was not obtained. Do not fabricate a second result with an identical or suspiciously close value -- examiners recognise the pattern and mark it as a procedural penalty.
7 | Five common errors
These five errors account for the majority of lost marks in Sec 3 and Sec 4 titration practicals.
1. Not rinsing the burette with the titrant before filling.
A burette that was washed with distilled water and not rinsed with the titrant will dilute the solution inside. The effective concentration of the titrant is lower than expected, so more volume is needed to reach the endpoint. Every titre in the experiment will be inflated by the same factor -- a systematic positive error. There is no way to correct this retrospectively.
Fix: rinse twice with the titrant immediately before filling, and drain through the tip.
2. Averaging the rough titration with the accurate values.
The rough result is a deliberate overshoot. It is recorded in the table as a reference point for the endpoint location, not as a measurement to be averaged. Including it in the mean produces an inflated titre and a downstream error in any concentration calculation.
Fix: mark the rough row "No" in the "Use for mean?" column and exclude it from all calculations.
3. Reading the top of a concave meniscus instead of the bottom.
For a concave meniscus (the normal case with aqueous solutions), the top of the curve is higher than the bottom. Reading the top gives a volume reading that is systematically larger than the true value. If you apply this error consistently to both the initial and final readings, the titre calculation may partially cancel the error -- but any inconsistency between runs (reading top for one, bottom for another) will produce non-concordant results that cannot be explained.
Fix: always position your eyes level with the meniscus and read the lowest point of the curve. Use a white card behind the burette to sharpen the contrast between the meniscus and the graduation marks.
4. Failing to expel the tip air bubble before the initial reading.
An air bubble trapped in the tip between the stopcock and the jet occupies volume. If it dislodges during the titration and is replaced by solution, that volume of solution appears to have been delivered to the flask but was not. The titre will be smaller than the true delivered volume -- a systematic negative error.
Fix: after filling, open the stopcock fully for two to three seconds to flush any bubble out. Confirm the tip is bubble-free before recording the initial reading.
5. Not recording the indicator endpoint colour change in the observations.
The endpoint is defined by the indicator colour change. If your observations table does not state the change -- for example, "solution in conical flask changed from colourless to pale pink (permanent)" -- the examiner cannot award marks for observing the endpoint correctly, even if your titre is accurate.
Fix: immediately after each titration run, write the colour change in your observations as a complete sentence. Include the word "permanent" to distinguish a true endpoint from a transient colour change.
8 | Indicator choice
The indicator is what makes the endpoint visible. In O-Level Chemistry 6092 titrations, two indicators appear on most practical papers.
Phenolphthalein
Phenolphthalein is colourless in acidic and neutral solution and turns pink in alkaline solution. When alkali is added to acid (or when the solution crosses from acidic to alkaline), the colour change is colourless to pink.
Practical tip: the endpoint using phenolphthalein is easiest to detect against a white tile. The first appearance of a pale pink colour that persists for at least 30 seconds on swirling is the endpoint. A deep pink colour means you have overshot by one or more drops.
Methyl orange
Methyl orange is red in acidic solution and yellow in alkaline solution. The endpoint colour is orange, but in practice the transition from yellow to the first permanent trace of orange (or red, depending on which direction you are titrating) is used.
Methyl orange gives a sharper colour change in acid solution. When you are adding acid to alkali (acid in burette, alkali in flask), the endpoint appears as the yellow solution turning to a permanent orange or faint red.
Quick selection rule:
Alkali in the burette, acid in the flask: phenolphthalein is the cleaner choice -- the colour change is colourless to pink, which is easy to detect visually. Stop at the first permanent pale pink.
Acid in the burette, alkali in the flask: methyl orange works well. Stop at the first permanent orange against a white tile.
If the question specifies an indicator, use that indicator. Do not substitute.
