970 CHAPTER 24: Some Nonmetals and Metalloids
like those of a metal or nonmetal? Defend your answer on
the basis of astatine’s location on the periodic table.
*70.Elemental chlorine is obtained by the electrolysis of molten
NaCl (Downs cell). Elemental fluorine is obtained by the
electrolysis of KHF 2 in a cell made of Monel metal (a stain-
less steel alloy). Both of these processes are dangerous.
Why?
*71.Acid rain consists of acids formed by the reaction of acid
anhydrides and water. List four acid anhydrides commonly
involved in acid rain formation and the sources of each.
*72.Sulfur deposits are mined by the Frasch process. Explain
why free sulfur is not found on the earth’s surface.
*73.(a) On the basis of electronic structures, explain why most
metal halides are ionic. (b) On the basis of your explana-
tion, predict which halide compounds are likely to be
covalent.
*74.(a) Which of the halogens is the most active chemically
and (b) which of the halogens is most likely to be reduced
from the free state? (c) Which of the halogens is most likely
to act as an oxidizing agent? (d) Which of the halogens is
least likely to be an effective oxidizing agent? (e) Which of
the halogens is likely to be a liquid under room conditions?
(f) Which of the halogens is found free in nature?
*75.The nitrogen cycle indicates that electrical storms (light-
ning) are a source of nitrogen compounds. (a) What is the
function of the lightning? (b) What compounds of nitro-
gen are produced during electrical storms? (c) What is the
effect of these compounds on the rain water?BUILDING YOUR KNOWLEDGE*76.Standard enthalpies of formation are 402 kJ/mol for
XeF 6 (s) and 261.5 kJ/mol for XeF 4 (s). Calculate H^0 rxn
at 25°C for the preparation of XeF 6 from XeF 4 and F 2 (g).*77.The average atomic mass of N is 14.0067 amu. There are
two isotopes which contribute to this average:^1407 N
(14.00307 amu) and^1507 N (15.00011 amu). Calculate the
percentage of^1507 N atoms in a sample of naturally occur-
ring nitrogen.
*78.The NmN and the NXN bond energies are listed in
Tables 15-2 and 15-3. Predict whether four gaseous nitro-
gen atoms would form two gaseous nitrogen molecules or
a gaseous tetrahedral molecule similar to P 4 , basing your
prediction on the amount of energy released as the mole-
cules are formed. Repeat the calculations for phosphorus
using 485 kJ/mol for PmP and 201 kJ/mol for PXP.
*79.Commercial concentrated HNO 3 contains 69.5 mass %
HNO 3 and has a density of 1.42 g/mL. What is the molar-
ity of this solution? What volume of the concentrated acid
should you use to prepare 10.0 L of dilute HNO 3 solution
with a concentration of 6.00 M?
*80.What is the total mass of silicon in the crust of the earth?
Assume that the radius of the earth is 6400 km, the crust
is 50 km thick, the density of the crust is 3.5 g/cm^3 , and
25.7 mass % of the crust is silicon.
*81.How many grams of xenon oxide tetrafluoride, XeOF 4 , and
how many liters of HF at STP could be prepared, assum-
ing complete reaction of 10.5 g of xenon tetrafluoride,
XeF 4 , with a stoichiometric quantity of water according to
the equation below?6XeF 4 (s)8H 2 O()88n
2XeOF 4 ()4Xe(g)16HF(g)3O 2 (g)*82.Argon crystallizes at 235°C in a face-centered cubic unit
cell with a5.43 Å. Determine the apparent radius of an
argon atom in the solid.
*83.A reaction mixture contained 100. g of K 2 MnF 6 and 174 g
of SbF 5. Fluorine was produced in 38.3% yield. How many
grams of F 2 were produced? What volume is this at STP?