Measuring Volume

Why this skill matters

Volume measurement appears on every Paper 5 and Paper 6 series. Whether you are mixing solutions for a rates experiment, measuring gas volumes, or performing a titration, the examiner expects you to choose the right apparatus and read it correctly. Marks are lost for parallax errors, wrong apparatus choices, and forgetting to state the resolution.

Method and technique

Measuring cylinder

The measuring cylinder is the general-purpose volume measurer. Available in sizes from 10 cm3 to 1000 cm3, it is suitable when high precision is not required.

1. Place the measuring cylinder on a flat, level surface.
2. Pour the liquid in slowly to avoid splashing.
3. Wait for the liquid to settle and the meniscus to form.
4. Bring your eye level to the surface of the liquid (not looking down or up).
5. Read the volume at the bottom of the meniscus for aqueous solutions.
6. Record to the nearest graduation (for example, to the nearest 1 cm3 for a 100 cm3 cylinder, or to the nearest 0.5 cm3 for a 50 cm3 cylinder).

Burette

The burette is used for titrations and delivers variable volumes with high precision.

1. Rinse the burette with the solution you will use (not water) to avoid dilution.
2. Fill the burette using a funnel, ensuring the space below the tap is also filled (no air bubbles).
3. Remove the funnel before reading.
4. Read the initial volume at eye level. Burettes read from top (0.00) to bottom (50.00).
5. Deliver the liquid by opening the tap. Near the end point, use half-drops.
6. Read the final volume. The volume delivered is final minus initial reading.
7. Record burette readings to the nearest 0.05 cm3 (for example, 23.50 cm3, not 23.5).

Pipette

The pipette delivers a single fixed volume with high accuracy.

1. Rinse the pipette with the solution you will use.
2. Use a pipette filler (never your mouth) to draw up the solution above the graduation mark.
3. Release slowly until the bottom of the meniscus sits on the graduation mark.
4. Touch the tip to the surface of the liquid in the receiving flask to deliver. Do not blow out the last drop unless the pipette is marked “blow out”.

Common errors and how to avoid them

Parallax error: Reading the meniscus from above or below eye level gives an incorrect reading. Always read at eye level. On Paper 6, state this explicitly: “read the volume at eye level at the bottom of the meniscus.”

Wrong apparatus for the job: Using a 250 cm3 measuring cylinder to measure 5 cm3 gives poor accuracy. Choose the smallest apparatus that fits the volume needed. A 10 cm3 measuring cylinder is more accurate for 5 cm3 than a 100 cm3 one.

Forgetting to rinse with solution: Rinsing a burette or pipette with water instead of the solution it will contain dilutes the first portion and affects the result.

Air bubbles in the burette: An air bubble below the tap will be released during the titration, making the volume reading too large. Check for bubbles before starting.

Marking points examiners look for

On Paper 5/6, when asked about measuring volume, include:

• The name of the apparatus chosen and why (accuracy, volume range)
• Read at eye level / at the bottom of the meniscus
• The resolution of the apparatus (e.g., burette to nearest 0.05 cm3)
• Repeat readings for reliability (especially in titration)