Measuring Volume: Beakers, Cylinders, Pipettes and Burettes

Measure out 25 cm³ of water with a beaker and weigh it. Then do the same with a measuring cylinder, a burette and a pipette. You’ll get four different answers, and only one or two of them will be close to 25.00 g. Choosing the right equipment, and using it properly, is one of the most important skills in practical chemistry. It’s the difference between a result that’s roughly right and one that’s genuinely reliable.

The options, from least to most accurate

Equipment	Typical capacity	Typical uncertainty	Best for
Beaker	50–1000 cm³	about ±5%	holding and mixing; very rough volumes only
Conical flask	100–500 cm³	about ±5%	holding solutions, titrations
Measuring cylinder	10–1000 cm³	about ±1% (e.g. ±0.5 cm³ on 50 cm³)	moderately accurate volumes
Graduated pipette	1–25 cm³	about ±0.5%	small, variable, accurate volumes
Burette	50.00 cm³	±0.05 cm³ per reading	variable volumes, titrations
Volumetric pipette	10.00, 20.00, 25.00 cm³	about ±0.06 cm³ for 25.00 cm³ (±0.24%)	one fixed, very accurate volume
Volumetric flask	100.0, 250.0 cm³	about ±0.2–0.3 cm³ (±0.1%)	making solutions to an exact volume

Values vary with the size and grade of the glassware. The details are in volumetric glassware tolerances.

The rule of thumb: the more precisely something is made to measure a single volume, the more accurate it is. That’s why a volumetric pipette (which measures one volume) beats a graduated pipette (which measures many).

Reading the meniscus

When water or an aqueous solution is in a narrow tube, its surface curves down in the middle. This curved surface is the meniscus. It forms because water molecules are attracted to the glass (adhesion) more strongly than to each other (cohesion), so the liquid creeps up the sides.

How to read it correctly:

1. Read from the bottom of the meniscus for water and most solutions.
2. Put your eye level with the meniscus. Looking from above or below shifts where the meniscus appears against the scale markings, so you read the wrong value. This is called parallax error.
3. Hold a white card with a black stripe just behind and below the meniscus. The black line reflects in the curve and makes the bottom much sharper.
4. Keep the equipment vertical. A tilted cylinder gives a wrong reading.

Exceptions: for mercury, which curves upwards, read the top of the meniscus. For very dark or opaque solutions (such as potassium permanganate), where you can’t see the bottom, read the top consistently for both initial and final readings.

Using a measuring cylinder

• Choose the smallest cylinder that will hold the volume. Measuring 8 cm³ in a 100 cm³ cylinder gives a much larger percentage error than using a 10 cm³ cylinder.
• Place it on a flat bench and bend down to read at eye level.
• Add the last small amount with a dropping pipette.
• Liquid clings to the inside, so it doesn’t deliver exactly what it reads. That’s fine for most purposes but not for accurate analysis.

Using a volumetric pipette

1. Rinse with distilled water, then with a little of the solution you’ll measure, and discard the rinsings.
2. Use a pipette filler, never your mouth.
3. Draw liquid above the calibration mark.
4. Let it fall slowly until the bottom of the meniscus sits exactly on the line, at eye level.
5. Wipe the outside of the tip if drops cling to it.
6. Let it drain freely into the receiving flask, then touch the tip against the inside of the flask.
7. Don’t blow out the small drop left in the tip. The pipette is calibrated to leave it behind.

Using a burette

1. Check the tap works and doesn’t leak.
2. Rinse with distilled water, then with the solution it will hold.
3. Fill using a small funnel, with the tap closed, below eye level (lower the burette or take it off the stand).
4. Remove the funnel before taking readings.
5. Run liquid through the tap to fill the tip and remove air bubbles.
6. Read to the nearest 0.05 cm³, and record two decimal places (for example 23.40, not 23.4).
7. Remember burettes read from the top down: 0.00 cm³ is at the top.

More on burettes in titrations is in acid–base titration and common titration errors.

Using a volumetric flask

1. Dissolve the solid (or add the measured liquid) in a beaker with less water than the final volume.
2. Transfer to the flask with a funnel, rinsing the beaker and funnel into the flask several times.
3. Add distilled water until just below the mark, then add the final drops with a dropping pipette until the bottom of the meniscus sits on the line.
4. Stopper and invert 10–15 times to mix. This step is often forgotten and causes big errors.
5. Don’t heat volumetric glassware or use it for hot liquids; heat can permanently change its volume.

Calculating percentage uncertainty

Uncertainty tells you how much a reading might differ from the true value. Percentage uncertainty lets you compare equipment fairly:

percentage uncertainty = (uncertainty ÷ value measured) × 100

Example 1: measuring cylinder. A 50 cm³ cylinder with uncertainty ±0.5 cm³, used to measure 25 cm³: 0.5 ÷ 25 × 100 = 2.0%

Example 2: volumetric pipette. A 25.00 cm³ pipette with uncertainty ±0.06 cm³: 0.06 ÷ 25.00 × 100 = 0.24%

Example 3: burette. Each reading is ±0.05 cm³. A titre uses two readings, so the titre uncertainty is ±0.10 cm³. For a titre of 22.50 cm³: 0.10 ÷ 22.50 × 100 = 0.44%

Example 4: small burette volume. For a titre of only 5.00 cm³: 0.10 ÷ 5.00 × 100 = 2.0%

The last example shows why experiments are designed to give larger titres: the fixed reading uncertainty becomes a smaller fraction of the total.

For combining uncertainties from several measurements, see calculating percentage uncertainty.

Temperature matters

Glassware is calibrated at a specific temperature, usually 20 °C, and marked as such. Liquids expand as they warm, and glass expands slightly too. For most school work the effect is negligible, but in precise analytical work solutions are brought to room temperature before measuring, and hot solutions are never put in volumetric glassware.

“TD” and “TC”

Some glassware is marked:

• TD (to deliver) or Ex: calibrated to deliver the stated volume when emptied correctly. Pipettes and burettes are TD.
• TC (to contain) or In: calibrated to contain the stated volume. Volumetric flasks are TC.

A TC flask holds exactly 250.0 cm³, but if you pour it out, a little liquid clings to the inside, so slightly less comes out.

Quick decision guide

You need to…	Use
Pour roughly 100 cm³ of water to rinse something	beaker
Measure about 20 cm³ of acid for a qualitative test	measuring cylinder
Measure exactly 25.00 cm³ of a solution for analysis	volumetric pipette
Add acid until an end point and know the volume	burette
Make up exactly 250.0 cm³ of a standard solution	volumetric flask
Measure 2.50 cm³ precisely	graduated pipette or burette

Key takeaways

• Beakers and flasks aren’t for measuring; measuring cylinders are moderately accurate; pipettes, burettes and volumetric flasks are the most accurate.
• Read the bottom of the meniscus at eye level, using a white card for contrast.
• Pipettes: rinse with the solution, fill with a filler, touch off, don’t blow out.
• Burettes: remove the funnel, clear air bubbles, read to 0.05 cm³.
• Percentage uncertainty = uncertainty ÷ value × 100; larger measured volumes give smaller percentage uncertainties.