Name _________________________
Chemistry 100
Exam 2 SOLUTION
Answer the following questions in the spaces provided. You must show your work to receive credit
for an answer. Showing your work also allows for maximum partial credit. Place your final answer,
with attention to significant figures and units, in the boxes provided.
1. Platinum is currently being researched as a carrier of hydrogen gas for fuel-cell technologies (even
though it is very expensive). It exists as 4 major stable isotopes (and 2 very minor ones), given in
the table below. Using the data, determine the average atomic mass of platinum. [10]
Isotope
% Abundance
Atomic Mass (amu)
Pt
32.97
193.962
195
Pt
33.83
194.964
196
Pt
25.24
195.965
198
Pt
7.163
197.968
194
Pt-194: 0.3297 x 193.962 amu =
Pt-195: 0.3383 x 194.964 amu =
Pt-196: 0.2524 x 195.964 amu =
Pt-198: 0.07163x197.968 amu =
average atomic mass =
63.95 amu
65.96 amu
49.46 amu
14.18 amu
193.55amu
Atomic mass = 193.55 amu
2. Fill in the missing values in the tables below. [9]
Atom
Name
Z
A
Protons
Neutrons
Electrons
Nb
Niobium
41
93
41
52
41
Se
Selenium
34
80
34
46
34
3. Determine the formula weight for: [8]
a. Gallium sulfide, Ga2S3
(2 x Ga) + (3 x S) = (2 x 69.723 amu) + (3 x 32.06 amu) = 235.63 amu
Formula weight = 235.63 amu
b. Aspirin, C9H8O4
(9 x C) + (8 x H) + (4 x O)=(9 x 12.011 amu) + (8 x 1.0079 amu) + (4 x 15.9996 amu) = 180.161 amu
Formula weight = 180.161 amu
Exam 2
Fall 2007
Page 1 of 4
Chemistry 100
Clark College
4. Write the electron configurations for the following elements and ions. You may use the shortcuts if
you want. Also, give the number of valence electrons for each species. [15]
Valence
electrons?
Configuration
a) Rh
[Kr] 5s24d7
9
b) S
[Ne] 3s23p4
6
c) Ga+3 Ga: [Ar]4s23d104p1
Ga+3 = [Ar]3d10
10 (or 0)
d) Fe+3
Fe: [Ar]4s23d6
Fe+3 = [Ar]3d5
e) P-3
P: [Ne]3s23p3
P-3 = [Ne]3s23p6 = [Ar]
5
8 (or 0)
5. Draw the orbital diagrams (boxes and arrows) for the valence electrons in Titanium (Ti). Based on
the electron configuration, what are the two most common charges for Titanium ions? Briefly
explain how you arrived at your answer. [8]
Ti = [Ar]4s23d2
!" ! !
4s 3d 3d 3d 3d 3d
Ti+2 = [Ar]3d2
Ti+4 = [Ar]
! !
4s 3d 3d 3d 3d 3d
4s 3d 3d 3d 3d 3d
6. Write the full atomic symbol for the element with 29 electrons and 35 neutrons. [4]
64
Cu
29
7. Write the full atomic symbol for mercury-202. [4]
202
Hg
80
8. Nomenclature. For the following sets of 4 compounds, do 3 of 4. You may do the 4th for extra
credit. Indicate which three you would like graded for credit by placing a star * next to them.
If no indication is made, the first three of each set will be graded for credit. [18+2]
a. Write the name of the compound based on the formula given.
Exam 2
mercury (I) phosphate
(Hg2)3(PO4)2
tin (IV) sulfide
SnS2
triphosphorus pentabromide
P3Br5
potassium sulfate
K2SO4
Fall 2007
Page 2 of 4
Chemistry 100
Clark College
b. Write the formula of the compound based on the name provided.
Platinum (III) bicarbonate
Pt+3 + HCO3- → Pt(HCO3)3
Ammonium nitride
NH4+ + N-3 → (NH4)3N
Sodium oxide
Na+ + O-2 → Na2O
Dinitrogen hexafluoride
N2F6 (binary compounds are based off of the prefixes)
Multiple Choice. Circle the choice that best answers the question statement. [4 each, 24 total]
9. Which of the following elements is a nonmetal?
a. Ga
b. F
c. Fe
d. Sn
10. Which of the following elements is an alkaline earth metal?
a. Fe
b. Na
c. Ba
d. U
11. What is the correct name of H2CO3 (aq)?
a. Hydrogen carbonate
b. Hydrocarbonic acid
c. Carbonate acid
d. Carbonic acid
12. Which of the following represents the correct orbital diagram for nitrogen?
1s
2s 2p 2p 2p
a. ↑↓ ↑↓ ↓
b. ↑↓ ↑↓ ↑
c. ↑↓ ↑↑ ↑
↑
↑
↑
↑
↑
↑
d. ↑↓ ↑↓ ↓↑ ↑
Exam 2
Fall 2007
Page 3 of 4
Chemistry 100
Clark College
13. Which of the following orbitals is a ‘p’ orbital?
14. The formula weight for diboron tetrachloride?
a. 81.71 amu
b. 163.42 amu
c. 198.89 amu
d. 416.4 amu
Exam 2
Fall 2007
Page 4 of 4