Burets

Reading Burets

You may wish to practice reading the buret by filling it with water and practicing reading the water level. You will note the liquid surface in the buret is curved. This surface is called the meniscus. Normally you will read the bottom of the curved surface as the volume reading. NOTE: To get a true reading you MUST hold your eye even with the liquid level. If you read from above or below the liquid level you will get an inaccurate reading (the effect is called parallax).

If a very dark liquid (such as a water solution of potassium permanganate) is put into the buret it may be impossible to see the bottom of the meniscus. In these cases you may read the top of the meniscus as the volume reading. As long as you read the buret this way each time the error will be negligible.

Running Liquids Out of the Buret

A finite amount of time is required for the liquid to drain down the walls of the buret so wait at least thirty seconds after you have shut off the stopcock before you read the volume. This statement also applies when you fill the buret with liquid. Allow some time for the liquid to run down the wall of the buret before you read the initial volume.

Two last important notes:

1. NEVER FLAME DRY A BURET OR PUT HOT LIQUIDS IN A BURET. The markings on the buret give the volume at the temperature specified on the buret (usually 20°C or 25°C). Heating will permanently change the volume of the device. Also, volumetric glassware is not Pyrex so it will probably break if heated. The above statements apply to all volumetric glassware (pipets, burets, volumetric flasks, graduated cylinders, etc.)

2. After finishing the titrations, drain burets completely. Rinse twice with tap water and once with distilled water. Return clean burets and unused acid and base to the place you got them from.