Lab Skills

Buret Reading

Read the bottom of an animated meniscus to ±0.01 mL. Practice single readings or volume delivered, with feedback on parallax and top-of-meniscus errors.

Meniscus0.01 mLVolume DeliveredPractice
Topic L.1

Reading a Buret and Titration Technique

Make observations or collect data from representations of laboratory setups or results, while attending to precision where appropriate.

A buret delivers a precisely measured, variable volume. Reading it correctly is worth real points on the free-response section.

Reading rules:

  • Read at the bottom of the meniscus, at eye level. Viewing from above or below introduces parallax error.
  • A buret graduated in 0.1 mL divisions is read to ±0.01 mL — one estimated digit beyond the smallest division.
  • Burets are numbered downward: 0.00 at the top. Volume delivered = final reading − initial reading.
  • Record both readings. Never assume you started at exactly 0.00 mL.

Procedure that affects results:

  • Rinse the buret with titrant before filling. Rinsing with water leaves residual water that dilutes the titrant, so more volume is needed and the calculated analyte amount comes out too high.
  • Remove the air bubble from the tip before the initial reading. A bubble that escapes during titration adds apparent volume, again inflating the result.
  • Rinsing the analyte flask with water is harmless — it changes concentration but not moles of analyte.
  • Overshooting the endpoint adds excess titrant, giving a result that is too high.

Key points

  • Read the bottom of the meniscus at eye level, to ±0.01 mL.
  • Volume delivered = final − initial. Record both.
  • Rinsing the buret with water (not titrant) makes the calculated analyte concentration too high.
  • Extra water in the analyte flask has no effect on the result.

Common mistakes

  • Reading the buret upside down. The scale increases downward.
  • Reporting a whole number of mL. A buret reading needs two decimal places.
  • Assuming any added water changes the answer. It matters in the buret, not in the flask.

Worked example

A student records an initial buret reading of 1.24 mL and a final reading of 27.86 mL. (a) What volume was delivered? (b) The student had rinsed the buret with distilled water and not with titrant. Explain the effect on the calculated concentration of the analyte.

(a) Volume delivered = 27.86 − 1.24 = 26.62 mL (both readings to ±0.01 mL, so the difference carries two decimal places).

(b) Residual distilled water in the buret mixes with the titrant, lowering its actual concentration below the nominal value. Fewer moles of titrant are delivered per millilitre, so a larger volume is required to reach the endpoint.

The student, however, calculates using the nominal (undiluted) concentration together with that inflated volume. The computed moles of titrant — and therefore the computed moles and concentration of analyte — come out too high.

Full notes for topic L.1 →