In this course you will use three types of precision calibrated glassware: burets, pipets and
flasks.
This type of calibrated glassware is usually referred to as volumetric glassware. This
precision
glassware is capable of measurements of volume that are good to four significant digits and is
consequently expensive. You should be careful in handling this type of equipment so that
breakage losses are minimized. Be particularly careful with the tips of pipets and burets.
The only volumetric glassware in your lockers are 50, 100 and 250 mL volumetric flasks.
These
are characterized by long slender necks with a graduation mark on them. Volumetric pipets are
stored in drawers on the west wall of the lab and the burets are kept in a cabinet on the wall near
the door to the weighing room. Any other glassware in your locker with graduation marks is
not
volumetric. Such equipment is machine-made and not individually calibrated. It can be
used for
less accurate measurements but should never be used when high, analytical accuracy is required.
It takes some practice to use volumetric glassware properly and before you begin using
such
equipment you should inspect the pieces of glassware you plan to use, washing them in the
Alconox solution provided if necessary, followed by rinsing first in tap water and then three or
four rinses with distilled water. It is usually not necessary to dry volumetric ware. As for reading
volumetric ware, take advantage of the Web links which illustrate
the proper use of a
buret
and
the proper use of a
pipet
You must never expose any volumetric
glassware to sources of heat since such exposure will adversely affect the calibration. Thus, you
must never dry any volumetric glassware in a drying oven.
It is important that the volumetric glassware be completely clean before you use it. It must
drain
in such a manner that a smooth film of solution adheres to the inside, there must be no beading or
droplet formation on the inside walls of the vessel. If you observe such droplets, wash the
glassware with small amounts of warm Alconox solution. If necessary use a brush. If Alconox
treatments do not suffice, it may be necessary to clean the glassware using other methods.
Contact your lab instructor if you feel that this is required.
Volumetric pipets and burets that have recently been cleaned will not be dry on the inside. Before you use such wet glassware it must be rinsed with small portions of the solution to be measured. If you don't know how this is done consult your instructor.