MODULE 2
CALIBRATION OF A PIPETTE
SKILLS TESTED: ORR, AI
INTRODUCTION: In this experiment, you will accurately determine the volume of a 10 cm 3 pipette which is
advertised as being 10cm3+/- 0.06 cm3 . This will be achieved by measuring the mass of water transferred by
the pipette, followed by calculating the volume of that mass of water using the known density of water.
Without calibration, a systematic error of unknown magnitude may exist.
PROCEDURE
1. Collect distilled water in a beaker and let it stand for about 15 minutes before measuring and recording the
temperature of the water.
2. Weigh the dry empty beaker on the balance.
3. Using the pipette filler, fill and discharge the pipette into the pre-weighed beaker. Weigh and record the mass
of the beaker or container. ENSURE THE BOTTOM OF THE BEAKER HAS BEEN DRIED
THOROUGHLY BEFORE WEIGHING IT.
4. Repeat steps 3 – 4 until you have results for 5 trials. N.B. You do not need to empty and dry the beaker
between trials.
5. After the experiment has been completed, measure and record the temperature of the water you have pipetted
and take the mean of the two temperatures you have measured. This value will be used as the temperature of
the water during the calibration.
6. Write a full lab report.
Treatment of results
1. Calculate the mean mass of water discharged of the five trials.
2. Using the values in the table below, plot a graph of density vs temperature and use the graph to
determine the density of the water you have used, based on its temperature.
X T/oC
26
28
30
32
34
36
Y Density /gcm-3 0.99678 0.99623 0.99565 0.99503 0.99438 0.99369
3.
4.
5.
6.
7.
Using your answer from question 2 determine the mean volume of water discharged from the pipette.
Calculate the standard deviation of the five masses from question 1 and convert to volume as well.
State the capacity of the pipette in the format:- mean volume ± standard deviation
State the capacity of the pipette as shown on the pipette you have used.
Using the mean volume you have calculated and true mean value stated on the pipette, calculate the %
error via the formula below
% error = difference between calculated mean value and true mean value x 100
true mean value
8. Discuss any sources of error in your experiment.
9. Comment on the accuracy and precision of the pipette you have used based on your results.