Procedure:
(1) If a semiautomated or automated pipette, adjust pipette to desired volume in mL.
(2) Weigh an empty beaker carefully on an accurate scale. This should be large enough to hold multiple replicate pipettings. Do not touch the beaker once it has been weighed.
(3) Dispense water at least 10 times into the beaker, recording the weight after each addition of water. Be careful to wipe the pipette accurately so as not to add or remove fluid. Determine the weight for each pipetting.
(4) Record the temperature of the water and determine the water density.
|
Water Temperature in °C
|
Density in g/mL
|
|
17°C
|
0.99880
|
|
18°C
|
0.99862
|
|
19°C
|
0.99843
|
|
20°C
|
0.99823
|
|
21°C
|
0.99802
|
|
22°C
|
0.99780
|
|
23°C
|
0.99756
|
|
24°C
|
0.99732
|
|
25°C
|
0.99707
|
(from Figure 1-3, page 29)
mean volume in mL =
= (mean weight of aliquot in grams) / (density of water for °C)
volume error in mL =
= (mean volume in mL) – (expected volume in mL)
volume error in percent =
= (volume error in mL) * 100 / (expected volume in mL)
Interpretation:
• The acceptable volume error should be determined for the procedures to be performed. Usually a volume error <= 3% is acceptable.
