EXPERIMENT
Measuring Liquid Volumes
Vol
The volume markings on beakers are very approximate (they are usually marked ±5%.) Graduated
cylinders are better, but still not good enough for accurate work. Most accurate of all are pipets, burets,
and volumetric flasks. In this experiment, you will learn to correctly use a buret and a volumetric pipet.
I. Using a Buret
A. Check For Leaks
Before you clean your buret, fill it with water, close the stopcock, and see if it leaks. Check for drops of
water appearing around the stopcock, or drops coming out of the buret tip even though it is closed. If it
leaks, return it and get another!
B. Cleaning--See general section on cleaning. This step is crucial!
C. Mount the buret in a buret holder (not some random clamp.) The buret should be perpendicular to the
earth's surface. Step back and view it from two different perspectives. You should be able to visually line
it up with lines in the room; it should run parallel to door sills, window sills, and room corners.
D. Fill the buret with solution to be used. Don’t overfill the funnel; you’ll end up with solution all over
the outside of your buret. Don't bother hitting 0mL exactly; something between 0 and 5 mL is fine. Get
rid of any air bubbles in the tip (you shouldn't see a meniscus there!)
E. Reading volumes:
1. At the interface between your liquid solution and the gas phase (air), you will observe a curved
surface called a meniscus. You read the volume at the very bottom of the meniscus. Make sure
you are looking at the meniscus on a level, not from above or below.
2. Remember, 0 is on top, 50 is on the bottom. All readings have 2 places after the decimal, and the
last place is more often non-zero than zero.
II. Using a Pipet
A. Do not accept a pipet with a broken or cracked tip.
B. Pick a bulb to use. You will not get liquid into the pipet bulb, but some of the students before you
were not so careful. Check to make sure no liquid is coming out of the pipet bulb.
C. Clean your pipet as directed in the General Cleaning section.
D. Squeeze the pipet bulb. Place it over the top of the pipet.
E. Pull the liquid up past the fill line, until the liquid is approximately halfway between the fill line and
the top of the pipet. DO NOT get liquid into the bulb! The bulb is full of all sorts of gross dried out stuff
from previous experiments, and if you get it wet it will leak all sorts of noxious stuff.
F. Remove the bulb and cover the top of the pipet with your index finger. This holds the liquid in place.
To allow liquid out of the pipet, rotate your finger slightly. Slowly drain the liquid until the meniscus is at
the fill line. (Note: this works best if your finger is slightly damp, but not wet.)
G. Empty the pipet contents into your destination flask. When the pipet stops draining, touch the pipet
tip to the glass (a little more will empty out.) There should be still a little bit left in the pipet. This last
little bit is supposed to stay in the pipet. DON'T blow it out.
III. General Cleaning Section
A. Check for obvious dirt; if there is some, get rid of it. Rinse well with tap water. Water should sheet
over inside surfaces. If the water beads up into little drops, there is an oily residue. If this is the case,
check with your instructor on how to clean with soapy water and a buret brush.
B. Rinse entire inner surface at least three times with small volumes (5mL) of deionized water. Discard
rinse water.
C. Rinse entire inner surface at least three times with small volumes of solution to be used. Discard rinse
solution.