CHEM 1412 Practice Problems
Chapters 20 & 21
Chapter 20
1. In each of the following reactions,
a) indicate the oxidation state of each element, and
b) identify which substance is oxidized and which is reduced.
1) BaSO4 (s) + 4C (s) à BaS (s) + 4CO (g)
2) 2Cu2+ (aq) + 2H2O (l) à 2Cu (s) + O2 (g) + 4H+ (aq)
3) 5H2SO3 (aq) + 2MnO4- (aq) à 5SO42- (aq) + 2Mn2+ (aq) + 4H+ (aq) + 3H2O (l)
2. Complete and balance the following equations:
a) Pb(OH)42- (aq) + ClO- (aq) à PbO2 (s) + Cl- (aq) (basic solution)
b) Tl2O3 (s) + NH2OH (aq) à TlOH (s) + N2 (g) (basic solution)
c) Cr2O72- (aq) + CH3OH (aq) à HCO2H (aq) + Cr3+ (aq) (acidic solution)
3. Sketch the voltaic cell based on the following reaction:
2Cr (s) + 3HSO4- (aq) + 9H+ (aq) à 3H2SO3 (aq) + 2Cr3+ (aq) + 3H2O (l)
Show a) the composition and charge of each electrode,
b) the composition of the solution in each compartment,
c) the direction of electron flow, and
d) calculate the value of Eocell (using reduction potentials from Appendix E).
4. Calculate the emf at 25oC of a cell that uses the reaction
Co (s) + I2 (s) à Co2+ (aq) + 2I- (aq)
when [Co2+ (aq)] = 0.016 M and [I- (aq)] = 0.0060 M (use Appendix E for standard
reduction potentials).
5. Given, Ni2+ (aq) + 2e- à Ni (s) Eored = -0.28 V
Cu2+ (aq) + 2e- à Cu (s) Eored = +0.34 V
which metal will oxidize more readily, copper or nickel?
6. A current of 5.0 amp is passed through molten Al2O3 for 24 hr. How many grams of
aluminum metal will form at the cathode of this electrolytic cell after this time?
Chapter 21
(From Brown, LeMay, and Bursten, Chemistry: The Central Science, 6th and 7th editions)
1. Indicate the number of protons and neutrons in the following nuclei:
a) 5626Fe b) 88Sr c) phosphorus-31
2. Identify and give the symbol of the following:
a) beta particle b) alpha particle
c) positron d) proton
e) neutron f) gamma ray
3. Write balanced nuclear equations for the following transformations:
a) iodine-131 undergoes beta decay
b) thorium-230 decays to a radium isotope
c) tungsten-181 undergoes electron capture
d) nitrogen-13 decays by positron emission
4. Predict the type of radioactive decay process for the following radionuclides:
a) 85B b) 6829Cu c) neptunium-241 d) chlorine-39
5. Indicate whether each of the following nuclides lies within the belt of stability (see figure
below, or in your textbook):
a) 10849In b) 10247Ag c) 177N d) 21086Rn
6. Which of the following nuclides would you expect to be radioactive? (You can refer to the
belt of stability again.)
a) 178O b) 17674W c) 10850Sn d) 9240Zr e) 23894Pu
7. Complete and balance the following nuclear equations by supplying the missing particle:
a) 3216S + 10n à 11p + ?
b) 74Be + 0-1e (orbital electron) à ?
c) ? à 18776Os + 0-1e
d) 9842Mo + 21H à 10n + ?
e) 23592U + 10n à 13554Xe + 2 10n + ?
8. Write balanced equations for
a) 23892U (n, g) 23992U b) 147N (p, a) 116C c) 188O (n, b) 199F
9. Harmful chemicals are often destroyed by chemical treatment. For example, and acid can
be neutralized by a base. Why can't chemical treatment be applied to destroy the
radioactive products produced in a nuclear reactor?
10. A sample of curium-243 was prepared. After 1.00 yr, the activity of the sample had
declined from 3012 disintegrations per second to 2921 disintegrations per second. What is
the half-life of the decay process?
11. Radium-226, which undergoes alpha decay, has a half-life of 1622 yr. How many alpha
particles are emitted in 1.0 min by a 5.0 mg sample of 226Ra?
12. An ancient wooden object is found to have an activity of 9.6 disintegrations per minute per
gram of carbon. By contrast, the carbon in living trees undergoes 18.4 disintegrations per
minute per gram of carbon. Based on the activity of carbon-14 (with a half-life of 5730 yr)
in the object, calculate its age.
13. How much energy must be supplied to break a single 168O nucleus into separate protons
and neutrons if the nucleus has a mass of 15.99052 amu? How much energy is required
per mole of this nucleus?