Chemistry 163
Harold
CALIBRATION OF VOLUMETRIC GLASSWARE
Chemistry 163 Laboratory
South Puget Sound Community College
Purpose
The purpose of this exercise is to accurately calibrate your 25 mL volumetric pipet and buret so
that in subsequent experiments, the volumes delivered will be known with greater accuracy than that
provided by the glassware manufacturers markings. The calibrations will be accomplished by measuring
the mass of water delivered by each of the pieces of glassware and converting those masses to volumes
based on the density of water at the delivery temperature.
Procedures:
Volumetric Pipet
If after the first trial with water the pipet retains droplets of water below the meniscus then clean
the pipet with micro-clean cleaning solution. A large graduated cylinder will be provided in one of the
hoods for this purpose. Rinse well with dH2O. The pipet should drain leaving no droplets in the pipet. If
it does not, try soaking the pipet in microclean solution while you calibrate the buret. If it still does not
drain properly speak to your instructor.
When clean, fill the pipet with dH2O at room temperature, such that the meniscus is precisely at
the calibration mark. Touch the tip of the pipet to the inside of a previously tared 50 mL Erlenmeyer
flask and allow the pipet to drain into the flask. Allow ~15 seconds to elapse after the pipet appears to
be empty. DO NOT shake the last bit out of the tip. ALWAYS use the same technique whenever using
the pipet. Measure the mass of water delivered in triplicate. Calculate the volume of water at room
temperature using interpolated density values determined from CRC published values of water density.
The range among the results should not exceed 0.03 mL The average value is the volume value you
should use whenever using your pipet. As always standard deviation and RSD should be included.
50 mL Buret
Clean the buret with a buret brush and rinse well. Fill to very near the zero mark (at or below).
Record an initial reading. Drain 10 mL into a tared 50 mL Erlenmeyer flask. Record the end level,
measure and record the mass of water delivered. Repeat this process two more times for the 0 - 10 mL
portion of the buret. Perform the same procedure in triplicate for 0 - 20 mL, 0 - 30 mL, 0 - 40 mL and 0 50 mL (DO NOT GO BELOW). Thus, each volume has been measured 3 times and an average variation
from the true should graphed. Calculate the volume delivered for each of the trials at each range.
Determine the variation from expected volume for each range. Create a correction graph. Vertical axis
will be the mL correction. Negative values (below zero) show volumes actually delivered are less than
buret values, positive show they are more. The horizontal axis will be the buret volumes 0, 10, 20, 30,
40, 50 mL. When you connect the points you have a calibration curve that can be used for any volume
delivered between 0 and 50 mL. A sample graph is shown below.
+.08
Buret Correction Table – add to measured values for true volume
+.06
+.04
+.02
-.02
10
20
30
40
50
-.04
-.06
-.08
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6/20/2007