59-320 Homework Assignment - Chapter 2
59-320 Homework - Chapter 2
Note: For Exercises, complete solutions are given at the back of the book, and
for Problems, only numerical answers are provided. The Exercises are the most
important to do, since they cover most of the major ideas. The Problems are
very short, usually hitting upon one concept at a time.
On differences between the 7th and 8th edition:
Chapter 2 in each edition is more or less the same, with a few minor numbering
changes in problems and figure numbers (see below).
Exercises
These first two problems use the buoyancy equation (eq. 2-1), which is used to
determine the true mass of a substance, which is the mass measured in a vacuum.
Since a standard mass in a balance is affected by buoyancy, it weighs less than it does
in vacuum (a buoyancy error occurs when the density of the object being weighed is not
equal to the density of the standard mass). If mass m′ is read on the balance, the true
mass of the substance weighted in vacuum is given by
⎛
ρ ⎞
m′ ⎜ 1 − a ⎟
ρw ⎠
⎝
m=
⎛
ρa ⎞
⎜⎝ 1 − ρ ⎟⎠
where ρa is the density of air (normally ca. 0.0012 g mL-1), ρw is the density of the
calibration weights (e.g., 8.000 g mL-1), and ρ is the density of the sample. Densities of
water are provided in Table 2.7 (8th edition) at the end of this handout.
2-A. What is the true mass of water if the measured mass in the atmosphere is 5.3974
g? When you look up the density of water, assume that the lab temperature is (a) 15°C
and (b) 25°C. Take the density of air to be 0.001 2 g/mL and the density of balance
weights to be 8.0 g/mL.
2-B. A sample of ferric oxide (Fe2O3, density = 5.24 g/mL) obtained from ignition of a
gravimetric precipitate weighed 0.296 1 g in the atmosphere. What is the true mass in
vacuum?
2-C. A solution of potassium permanganate (KMnO4) was found by titration to be
0.05138 M at 24°C. What is the molarity when the lab temperature drops to 16°C?
2-D. Water was drained from a buret between the 0.12- and 15.78-mL marks. The
apparent volume delivered was 15.78 − 0.12 = 15.66 mL. Measured in the air at 22°C,
the mass of water delivered was 15.569 g. What was the true volume?
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59-320 Homework Assignment - Chapter 2
2-E. Reproduce the spreadsheet in Figure 2-23 and the graph in Figure 2-24. (7th Ed.:
Fig. 2-19 and 2-20 - not 2-21: this is a typo).
Problems
Safety and Lab Notebook
Easy, quick, do them!
2-1, 2-2, 2-3, 2-4, 2-5
Analytical Balance
2-7, 2-9, 2-12
Glassware and thermal expansion
Easy
8th: 2-14, 2-15, 2-16, 2-17
7th: 2-14, 2-15, 2-16, 2-17, 2-18 (these are 2-17 combined from 8th)
Moderate
8th: 2-21, 2-24, 2-26, 2-27
7th: 2-21, 2-24, 2-25, 2-26
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59-320 Homework Assignment - Chapter 2
Table 2.7, D.C. Harris, 8th edition, Densities of water
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