CHEM 1A: Exam 1 Practice Problems:
These practice problems are not a comprehensive list of all questions to be asked on the exam. Refer to the suggested textbook HW, other
practice problems on the review page, iclicker questions, & challenge problem sets for a comprehensive review.
Unit Conversions & Dimensional Analysis:

65.3 g of Iron → _______________ mol Iron

3.97 x 1012 CO2 molecules →_______________ mol CO2

0.783 mol of CH3CH2OH →_______________ mL of CH3CH2OH

The density of a sample of propane (C3H8) gas is 1.80 g/L. How many molecules of propane are contained in a 1.50 L
balloon? What about the total number of atoms?

1.097 x 10-2 nm-1 → _______________ m-1

True or False: A gram of magnesium contains more atoms than a gram of calcium.
Reference Information: Density = 0.789 g/mL
Each conversion below involves at least one mistake. Can you identify the mistakes and correct them?
Corrected Conversions:

5.98 𝑚𝑜𝑙
𝐿
1𝐿
1 𝑚𝐿
10−3 𝑚𝐿 1 𝑐𝑚3
= ?
𝑚𝑜𝑙
𝑐𝑚3
________________________________________________________________________________________________________________________________________________________________________________________________________________________

0.087 𝑛𝑚
1𝑚
1 𝑚𝑚
1
10−9 𝑛𝑚
103 𝑚
= ? 𝑚𝑚
________________________________________________________________________________________________________________________________________________________________________________________________________________________

7.874 𝑔 1 𝑘𝑔 (10−2 𝑐𝑚)3
𝑐𝑚3
10−3 𝑔
(1 𝑚)3
= ?
𝑘𝑔
𝑚3
Nomenclature & Formulas
 Which of the following compounds contains the cation with the highest charge?
CuCl2
BaCl2
Na3PO4
Fe(NO3)3

Complete the table below.
Formula
Name
CaCl2
Calcium Chloride
Mg3(PO4)2
Magnesium phosphate
Co(MnO4)2
Cobalt (II) permanganate
Fe2S3
Iron (III) Sulfide
H2SO3
Sulfurous acid
HClO
Hypochlorous acid
P4O10
Tetraphosphorus decoxide
N2O5
Dinitrogen pentoxide
Atomic Theory & Nuclear Chemistry

Complete the table below.
Notice some of the elements are charged.

Naturally occurring Germanium consists of the five isotopes below, & has an average atomic mass of 72.63 amu.
Circle the isotope that is most abundant, or F) if insufficient information is provided.
Germanium Isotope
Isotopic Mass (amu)
A)
Germanium-70
69.92
B)
Germanim-72
71.92
C)
Germanium-73
72.92
D)
Germanium-74
73.92
E)
Germanium-76
75.92
F)
The most abundant isotope cannot be determined from the information provided.
Mass spectrometry data would have to be collected and analyzed.

There are three major isotopes of magnesium; 24Mg (mass = 23.985 amu), 25Mg (mass = 24.986 amu), and 26Mg
(mass = 25.983 amu). 24Mg represents 78.99% of all naturally occurring magnesium. Calculate the percent of
naturally occurring magnesium that is 25Mg.
Write the equation for the nuclear reaction described in each of the following processes:

Plutonium-238 (238Pu) undergoes alpha decay (used as an energy source in pacemakers, space craft, & other
applications where conventional power sources fail)

Carbon-14 (14C) undergoes normal beta decay (β-) (used in radio-carbon dating)

Fluorine-18 (18F) undergoes positron emission (β+) (one of the radionuclides used in PET scans)

Chromium-51 (51Cr) undergoes electron capture (a diagnostic radioactive tracer used to study blood)
Quantum Mechanics
 An electron falls from the n =7 to the n = 3 energy level in a hydrogen atom. Calculate the wavelength of the photon
that would be emitted in this electronic relaxation in nanometers (nm).

To which energy level diagram does the emission spectrum below correspond? Explain your reasoning by drawing all
possible relaxations that would occur with the energy level diagram, and indicate the associated emission signals.
A.
B.
C.
D.
E.

An object was radiating monochromatic light at a frequency of 2.947 x 1014 Hz. The total energy emitted per second
was 1.953 x 10-9 J. How many photons were emitted per second?

Four different metals (Cadmium, Cobalt, Chromium, and Sodium) were exposed to light with a wavelength of 121.2
nm. Given the threshold frequencies for the four metals, which metal will have an electron ejected with the highest
velocity?
Cd (νt = 9.86 x 1014 Hz)
Co (νt = 1.21 x 1015 Hz)
Cr (νt = 1.09 x 1015 Hz)
Na (νt = 5.77 x 1014 Hz)

The energy required to remove a single electron from the surface of zinc is 6.89 x 10-19 J. What is the longest
wavelength of light capable of ionizing zinc?

Monochromatic light with a frequency of 3.587x1015 Hz was shone onto the surface of Gold. Electrons were ejected
with a kinetic energy of 8.970x10-19 J. Calculate the work function of Gold in kJ/mol.

Identify any combination of quantum numbers below that is NOT allowed.
o n = 6, l = 5, ml = 0, ms = -½

o
n = 3, l = 0, ml = 0, ms = +½
o
n = 6, l = -5, ml = 0, ms = -½
o
n = 4, l = 0, ml = 4, ms = +½
o
n = 3, l = 0, ml = 0, ms = 0
For each orbital below, specify the number of angular nodes, & radial nodes. Based on this information, identify the
orbital designation (1s, 2s, 2p, 3s, 3p, etc.). In other words, determine the two quantum numbers (n & l) for each
orbital.