CALIBRATION
of
Volumetric Glassware

Experimental science frequently requires accurate
measurement of volumes.
A number of specialized pieces of laboratory glassware have been designed and created to deliver or contain volumes of water accurate to about 0.01 mL.
Those which you will use this semester are:
Volumetric Pipets
Graduated Pipet
Buret
Volumetric Flasks
Note they all have narrow sections where the volume is actually measured so that errors in filling, emptying or reading result in minimal errors in the actual volume measured.

   Like many things which have absolute values assigned to them by impersonal others, we frequently take for granted that a 5.00 mL pipet actually does deliver 5.00 mL of liquid. But should we? And does it????
   In this experiment, you will find out.
Delivering accurate volumes of liquid requires two things:
  1. A device of high accuracy to deliver the liquid.
  2. An operator of sufficient skill to use the device properly.

This experiment is not only a test of your glassware, but also a test of your technique.
...
THE PROCEDURE
SAFETY
Never mouth pipet! Use a rubber bulb to suck up the liquid into a pipet!
Hold the pipet and rubber bulb properly so the pipet does not break and cut you!

   You will deliver "exact amounts" of water from your buret and pipets relying on the manufacturer's calibration. But as a check, the amount of water delivered will also be measured by weighing this water.
   The manufacturer supposedly has calibrated the volume delivered by your pipet or buret to .01 ml.  You will use an Analytical Balance and weigh the water delivered to .0001 g.  0.0001 g represents the mass of approximately 0.0001 mL!
   Using the Specific Volume of water, you will convert the measured mass of water to volume. Using a thermometer to measure the temperature of the water used, you can approximate a very exact specific volume of water at your temperature. From this and the weight of water, you can determine the volume actually delivered.

CAUTIONS
The equipment must be clean and grease free.
The water delivered must not be allowed to evaporate before weighing.
Use distilled water. 

CORRECTIONS
A Buret Correction or a Pipet Correction is defined as....
What you must ADD to the the volume you thought you delivered (from the calibration markings on the equipment) to get the volume you actually delivered (calculated from the mass of the water).
A Buret or Pipet CORRECTION has...

  • SIGN ... it can be positive or negative.

  • SIG. FIGS. ... the number of sig figs in a correction derives from the accuracy of your experimental work and the accuracy assigned by the manufacturer to the pipet or buret. It is NOT arbitrarily assigned!

  • UNITS ... afterall, it is a volume which is added to a volume.

© R.W. Kluiber 1997; 1/15/2001