Chemistry Reference
In-Depth Information
Practice Problem 10.30
How many moles of barium ions and how
many grams of barium chloride would be required to produce 6.11 g of barium
sulfate?
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The masses of individual ions are important in food chemistry. For exam-
ple, too much sodium in the diet may be harmful to our health. Since it
doesn't matter much what anion is present, the quantity of sodium is given
on package labels. The general public, however, is not familiar with
moles, so the mass of sodium is stated as part of the nutritional informa-
tion on packaged foods.
The mass of a metal ion is essentially that of the atom, since the elec-
trons have such a small fraction of the mass of the atom.
ITEM OF INTEREST
EXAMPLE 10.31
(a)
Calculate the percent difference between the mass of a sodium atom and
a sodium ion.
(b)
Compare this percentage to those for a lithium atom and ion as well as
for a beryllium atom and ion.
Solution
(a)
The difference is the mass of an electron, 0.000549 amu.
0.000549 amu
23.0 amu
100%
0.00239%
(b)
For lithium:
0.000549 amu
6.94 amu
100%
0.00791%
For beryllium, which has lost two electrons:
2
0.000549 amu
9.01 amu
100%
0.0122%
The difference is very small indeed.
Snapshot Review
❒
The mass of only the cations or only the anions in a compound
cannot be measured on a balance.
❒
The mass of an ionic compound cannot be calculated from its number
of moles unless the identity of both ions is known.
ChemSkill Builder 5.3
Ag
,
A. A solution is treated with 0.400 mol of whereupon AgCl precipitates
and 0.013 mol of remains unprecipitated. (a) What fraction of a
mole of chloride ion was present in the original solution? (b) What
Ag
