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Homework 6 - Chem221 Fall 2013
Name______________________________________
Where applicable, please show all work to receive full credit.
Do not use theinternet to answer these questions, as it will not
help you on an exam. Due onDecember 4that the beginning of
class.
1. [2 points] Is there a difference between formal charge and
oxidation state? Ifso, explain.
2. [5 points] Use the Lewis structures to determine the
oxidation state of all atomsin the following compounds:
a. H2Sb. SCl2c. ClF3d. POCl3e. COS
3. [8 points] Balance the following redox reactions:a. Fe3+(aq)
+ I(aq)Fe2+(aq) + I2(aq) (acidic conditions)b. HNO3(aq) +
Cu(s)NO2(g) + Cu
2+(aq) (acidic conditions)c. Ce4+(aq) + I(aq)Ce3+(aq) + IO3
(aq) (basic conditions)d. V(s) + ClO3
(aq)V2O74(aq) + Cl(aq) (basic conditions)
4. [10 points] Use the Latimer diagrams in Resource Section 3 to
construct Frostdiagrams for the following:
a. Molybdenum in acidic solution (MoO3, MoO2, Mo3+, and Mo)
b. Chromium in acidic solutionc. Vanadium in acidic and basic
solution
5. [10 points] Given the following standard potentials in basic
solution
CrO42(aq) + 4 H2O(l) + 3 e
Cr(OH)3(s) + 5 OH(aq) E= -0.11 V
[Cu(NH3)2]+(aq) + eCu(s) + 2 NH3(aq) E= -0.10 V
And assuming that a reversible reaction can be established on a
suitable
catalyst, calculate Grxn and K for the reductions of (a) CrO42
and (b)
[Cu(NH3)2]+. Comment on why Grxn and K are so different between
the two
cases despite the values of Ebeing similar. Assume 25 C.
6. [3 points] Use the Latimer diagram in Resource Section 3 to
identify which
species are unstable with respect to disproportionation for
bromine in acidicsolution. Are any of the species unstable with
respect to comproportionation?
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Homework 6 - Chem221 Fall 2013
7. [5 points] Write the Nernst equation for
(a) The reduction of O2to water(b) The reduction of Fe2O3(s) to
Fe(s)
In each case express the formula in terms of pH. What is the
potential for the
reduction of O2at pH = 7 and p(O2) = 0.20 bar? Assume 25 C.
8. [3 points] Use standard potentials as a guide to write
equations for the following:a. N2O is bubbled into NaOH(aq)b. Zn(s)
is added to NaI3(aq)c. I2(s) is added to excess HClO3(aq)
9. [4 points] Adding NaOH(s) to Ni2+(aq) leads to the formation
of Ni(OH)2(s). Thestandard potential of the Ni2+/Ni couple is +0.26
V and Ksp= 1.5 x 10
16 M3. Whatis the electrode potential at pH = 14?
