Reading: Burets Revised 3/20/12

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BURETS

A buret is a piece of volumetric glassware used to deliver variable liquid amounts typically for

titrations. It is a long glass cylinder open at one end and fitted at the opposite end with a

stopcock valve (Figure 1). The stopcock valve controls the flow of liquid from the cylinder

through the buret tip. The buret used in the General Chemistry lab has a 50-mL volume and a

Teflon stopcock requiring no lubrication. The buret is etched with calibration markings at 0.10-

mL intervals allowing the estimation of variable liquid levels to the hundredths of a milliliter

(0.00 mL). Record all numbers from markings and one number estimated between markings

(significant figures) to indicate the sensitivity of the volume measurement.

Figure 1. Buret Use.

Reading: Burets Revised 3/20/12

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The numbering of the markings begins at the top (open end) of the buret. Therefore, the volume

delivered can be determined from the difference between initial and final liquid levels. Refer to

Figure 1 and note the correct way to read the liquid level in a buret (from the top down).

Before use, a buret should always be cleaned and prerinsed with the solution to be delivered.

Do NOT attempt to fill a buret precisely to the 0.00-mL mark at the top. This is a waste of time,

as all volumes delivered by a buret are determined from the difference between initial and final

readings. After filling the buret with solution, drain a few milliliters of liquid through the

stopcock into a beaker to remove any air bubbles trapped in the valve. Close the stopcock, tap

the buret sides gently, and allow the liquid to stand for a few minutes to clear gas bubbles

dissolved in the liquid. Remove any drop hanging from the buret tip by touching the tip to the

side of the beaker or wiping the tip with a tissue. Read the initial volume to the hundredths place

(0.00 mL).

To transfer the liquid, open the stopcock valve until the desired amount of liquid is slowly

drained into a container. Close the valve and touch off the hanging drop of liquid on the buret tip

adding it to the liquid in the container. This step is important because the hanging drop is part of

the volume delivered by the buret. Allow a moment for liquid on the cylinder walls to settle

before recording the final volume to ±0.01 mL (again from the top down). The difference

between the initial and final volumes is the amount of liquid transferred to the container.

Buret Care • Wash the buret with a mild dilute soap solution. Rinse first with tap water, and then

deionized (DI) water. If beads of water form on the walls, rewash.

• Never dry a buret in an oven! The heat will distort the glass and change the calibrated

volumes. Never dry a buret using air jets! The air system contains oil droplets and fine dust,

also the compressed air can break the glass.

• A buret should always be rinsed with a small amount of the solution to be used. This step

prevents contamination or dilution of the solution from water or other chemicals on the

glassware’s inside walls and removes the need to dry the buret.

Reading: Burets Revised 3/20/12

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• After an experiment is completed, drain all chemicals from glassware, pouring them into

marked collection containers in the hoods. Glassware may become irreversibly etched from

prolonged contact with some solutions (especially NaOH or KOH solutions). Wash the

glassware, rinse thoroughly, and return to common storage area at the front of the laboratory.

• Return all broken or cracked glassware to the stockroom for replacement.

Review Questions:

• When reading a buret, are the numbers read from the bottom up or the top down?

• When recording a buret volume, how many places past the decimal point should be

recorded?

• Why are the sides of the buret tapped after filling it?

• Why are a few milliliters of liquid drained through the tip after filling the buret?

• After delivering a certain volume into a flask, a drop of liquid is hanging from the tip. Is it

part of the delivered volume? Should it be added to the flask?