CALIBRATION of an Analytical Volumetric-ware
General directions
All volumetric ware should be freed of water before being calibrated. The water
used for calibration should be in thermal equilibrium with its surroundings. This
condition is best attained by drawing the water in advance, noting its
temperature at frequent intervals, and waiting until no further changes occur.
An analytical balance is used for calibration, weighing bottles serve as
receivers for the calibration liquid.
Calibration of a Volumetric Pipet
1) Determine the mass of the empty stoppered weighing bottle to the ±0.1 mg.
2) Transfer a portion of temperature-equilibrated water to the
weighing bottle with the pipet, weigh the bottle and its contents to ±0.1 mg.
3) Calculate the mass of water delivered from the differences in these masses.
Calculate the volume delivered with the aid of Table 28-3 (Skoog West &
Holler, 6th edition)
4) Repeat the calibration process 5 more times; calculate the mean value and
its standard deviation.
Calibration of a Buret
1) Fill the buret with temperature-equilibrated water and make sure that no air
bubbles are trapped in the tip. Lower the liquid level to bring the bottom of the
meniscus to the 0.0-ml mark. Wipe the tip of the buret with a paper tissue to
remove any adhering drop.
2) Weigh a 125-ml erlenmeyer flask fitted with a stopper to ±0.1 mg.
3) Transfer about 10 ml of water to the flask, touch the tip of the buret to the
wall of the flask. Record the volume that was apparently delivered, and refill
the buret.
4) Weigh the flask and its contents to ±0.1 mg; the difference between this
mass and the initial value gives the mass of water delivered. Use Table 28 -3 to
convert this mass to the true volume. Subtract the apparent volume from the
true volume. This difference is the correction factor that should be applied to
the apparent volume to give the true volume.
Repeat the calibration process 5 more times. Calculate the- mean value for the
correction factor.
5) Starting again from the zero mark, repeat the calibration; this time d elivering
about 20 ml to the receiver.
6) Test the buret at 10-ml intervals over its entire volume. Prepare a plot of the
correction to be applied as a function of volume delivered. The correction
associated with any interval can be determined from this plot.
DATA
CALIBRATION of a BURET
Empty flask weights:
1) ................. gr
2) .................gr
4) ................. gr
5) ................... gr
3) ................... gr
Flask + its contents weights (indicate the volume of water delivered from
the buret :.............. ml)
1) ................. gr
2) ...................gr
4) ................. gr
5) ................... gr
3) ................... gr
Mass of water delivered:
1) ................. gr
2) ...................gr
4) ................. gr
5) ................... gr
3) ................... gr
True volume:
1) ................. ml
2) ...................gr
4) ................. ml
5) ................... gr
3) ................... ml
[ True Volume - Apparent Volume] (correction factor)
1) ................. ml
2) ...................gr
4) ................. ml
5) ................... gr
3) ................... ml
Mean value for the correction factor : .................... ml
DATA
CALIBRATION of a PIPET
Empty bottle weigths:
1) ................. gr
2) ...................gr
4) ................. gr
5) ................... gr
3) ................... gr
Bottle + its contents weights:
1) ................. gr
2) ...................gr
4) ................. gr
5) ................... gr
3) ................... gr
Mass of water delivered:
1) ................. gr
2) ...................gr
4) ................. gr
5) ................... gr
3) ................... gr
Volume delivered:
1) ................. ml
2) ...................gr
4) ................. ml
5) ................... gr
3) ................... ml