1
EXPERIMENT 1
VOLUMETRIC WARE, DENSITY OF A LIQUID
07F
You may do either part A or part B first. To reduce the congestion at the balances, about
half of the class should do part A first while the other half does part B first.
A.
CALIBRATION OF VOLUMETRIC WARE
:
See Harris, Chapter 2.
You will use volumetric glassware in this laboratory and in subsequent laboratories.
Consequently, you must learn the use and precision of standard volumetric ware.
1.
A pipet is designed to deliver
a fixed volume of liquid. Use distilled water to
determine the volume of a pipet.
Measure the temperature of the distilled water (to ± 0.1
°
C) and
use the correct density of water (Harris, Table 2.7 with interpolation or better Eq. 2.4, p. 3334)
to calculate the volume of water delivered from the pipet. {You may use your calculator or Excel
to calculate the density of water at the temperature of your measurements.}
Weigh (Mass) a small beaker or vial.
Use a toploading balance (
±
1 mg) for these
experiments, not an analytical balance (
±
0.1 mg).
Carefully transfer the correct volume of
water from the pipet.
Do not
blow the last drop of liquid from the pipet.
Touch the tip of the
pipet to the side of the beaker or vial.
Weigh the receiver plus liquid.
Some volumetric pipets
are calibrated to deliver only a volume of liquid with free drainage. Some pipets have
graduations on the sides and the volume delivered is determined by allowing the liquid to flow to
the appropriate mark on the side.
With this type of pipet, you should not
let the liquid flow past
the 1.00mL (or X.00mL) mark.
Pay attention to the pipet that you are using.
Repeat the delivery and weighing
five
times.
It is not necessary to use a clean dry
receiver for each trial if you perform the experiment properly, but you must weigh the container
before each addition of liquid.
The data for replicate experiments should/will not be identical.
Do not transfer the liquid to the vial (beaker) while the vial (beaker) is on the balance!
Top
loading and analytical balances are expensive and sensitive pieces of equipment. Spilled
solutions and spilled solids will corrode a balance and cause it malfunction.
Apply the buoyancy correction (Harris, Eq. 2.1, p. 24) to each of your weights of water.
The correction is small, ~ 0.1 % or ~ 1 ppt of the measured weight (mass). Since the buoyancy
effect acts to reduce the mass, your corrected masses should be slightly larger than the measured
masses (note the example in Harris).
Calculate the density of water at the temperature of your experiments (Harris, Eq. 2.4, p.
33), and then calculate the volume of water delivered by the pipet. There is perhaps some
ambiguity about “T” in Eq. 2.4:
o
C or K.
However, you can easily determine which by
comparing your calculations with those in Table 2.7. Because the density of water at the
temperature of your measurements is less than 1, the volume of water delivered will be
numerically larger
than the weight of water, although only slightly.
Calculate the average and standard deviation of this set of measurements. {Harris, pp. 54
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 Fall '07
 Munson
 Chemistry

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