Honors Chemistry
Unit 15 and 16 Review
Concepts to know:
Unit 15: electrochemistry
Find oxidation numbers
Find what is being reduced (gains electrons/reduce charge) and oxidized (lose electrons and gains
charge) in a redox reaction
Be able to tell if a reaction is redox and if it is spontaneous or nonspontaneous (reactant being reduced
needs to be a bigger number than the one being oxidized on the reduction potential chart)
Understand an electrochemical cell- what direction electrons flow, cathode, anode, where cations go,
where anions go, why electricity is produced
Find the cell voltage of an electrochemical cell
Unit 16: nuclear chemistry
Know why some elements are radioactive
Alpha decay- know the symbol and how to balance a reaction with alpha decay
Beta decay-know the symbol and how to balance a reaction with beta decay
Gamma rays- pure energy; know the symbol; this is released when elements decay
Penetrating power: alpha < beta < gamma
Half life- the time it takes for ½ of radioactive material to decay
Fission- a heavy nucleus splits into 2 smaller nuclei of intermediate mass creating energy
Fusion- 2 light mass nuclei combine to form 1 heavier nucleus creating energy
Study the concepts on the 6 standard reviews
Practice problems
1. Given the following unbalanced equation:
KMnO4(aq) + HCl(aq) + Al(s) AlCl3(aq) + MnCl2(aq) + KCl(aq) + H2O(l )
a. If this reaction were to take place in an electrochemical cell, calculate the
voltage
b. What is being reduced and what is being oxidized? reduced: Mn oxidized: Al
c. Is the above reaction a spontaneous redox reaction? Explain your answer. Yes, the one getting reduced has a
higher reduction potential than the one being oxidized
2. All the following equations involve redox reactions except .
(a) CaO H2O Ca(OH)2
(b) 2SO2 + O2 2SO3
(c) 2HgO 2Hg +O2
(d) SnCl4 + 2FeCl2 2FeCl3 + SnCl2
3. Assign the correct oxidation number to the individual atom or ion in the following:
a. Mn in MnO2 +4
b. S in S8 0
c. Cl in CaCl2 -1
d. I in IO3 - +5
4. In an electrochemical cell, electricity is produced because of
(a) ionization (b) ion migration
(c) electron migration
e. C in HCO3 - +4
(d) proton migration
5. Use the diagram of the voltaic cell to answer the following questions.
a. Write the anode half-reaction. Ni  Ni2+ + 2eb. Write the cathode half-reaction. Cu2+ + 2e-  Cu
c. Write the balanced cell reaction. Cu + Ni2+  Cu2+ + 2Ni
d. Do electrons within the voltaic cell travel through the
voltmeter in a clockwise or counterclockwise direction? clockwise direction
e. Do anions in the beaker pass through the salt bridge in a
clockwise or counterclockwise direction? Counter clockwise
f. Calculate what the cell voltage? 0.59 V
g. which electrode will gain mass? copper
6. Write a balanced equation for each of the following
a. Argon-37 goes through beta decay 37Ar  0e + 37 K
244
b. Pu-244 goes through alpha decay
Pu  4He + 240 U
7. Which nuclear symbol matches an element that has 18 protons and 21 neutrons?
a. Ar
b. Ar
c. Ar
d. Al
18
21
18
21
39
39
18
39
8. The half-life of iodine-131 is 8.040 days. What percentage of an iodine-131 sample will remain
after 40.2 days? 0.03125% (1/32)
9. Uranium-238 decays through alpha decay with a half-life of 4.46 x 109 years. How long would
it take for 1/8 of a sample of uranium-238 to remain? 1.34 x 1010 years
10. A rock sample contained 5.0 g of In-115. The half-life of In-115 is 4.0 days. Determine the time
when only 1.25 g of In-115 remains. 8 days
11. The half-life of a radioactive isotope is 6.0 hours. After 8 half-lives, how much of a 1.0-mg sample
will remain? 3.9 x 10-3 g
12. Which process is occurring during the reaction represented by this equation?
a. beta decay
b. gamma emission
c. alpha decay
d. the gaining of a positron
50
120
Sn He +
2
4
48
116
Cd
13. Nuclear fission is different from fusion in that
a. fusion releases energy because nuclei are broken up.
b. fission releases more energy per gram of fuel than fusion.
c. fusion is more difficult to accomplish at low temperatures.
d. fission involves the combining of small nuclei.
14. Compare the mass, charge, and penetration power of alpha, beta and gamma radiation.
Mass
Charge
Penetration
Alpha
4
+
Lowest
Beta
0
-
Middle
Gamma
0
0
Highest
15. Why does an atom undergo radioactive decay? Because it has an unstable nucleus
16. Compare and contrast fission and fusion. Why is fission used for electrical and fusion is not?
Fission=Division, the splitting of large unstable atoms(nucleus)
Fusion=joining together, small isotopes of H, creates way more energy; hard to do at lower
temperatures
17. What is different about nuclear reactions when compared to a chemical reaction?
Nuclear reactions transform atoms into other atoms, chemical reactions involved the rearrangement
of electrons
Use the paragraph below to answer questions 18-21.
The first atom of element 112 was created and confirmed by a research team in 1996. The element was created by
bombarding lead foil with highly ionized zinc atoms. The single atom of the new element decayed after 280
microseconds, losing an alpha particle to form element 110.
18. What is the symbol for element 112? Uub
19. Write the chemical symbol and name of an element whose chemical properties are likely to be similar to those of
element 112? Explain your answer.
Any element in Group 12, so Zn, Cd, or Hg
20. Show how a combination of the atomic numbers of zinc and lead could account for the formation of a nucleus of the
new element described in the passage.
30Zn and 82Pb = 112Uub
21. Write the equation to show the radioactive decay of
227
112
223
Uub  24 He + 110
Kr
227
112
Uub as described in the passage.