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

12  3.97 x 10 CO2 molecules →______mol CO2

 0.783 mol of CH3CH2OH →______mL of CH3CH2OH Reference Information: Density = 0.789 g/mL

 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.

Each conversion below involves at least one mistake. Can you identify the mistakes and correct them? Corrected Conversions: 5.98 푚표푙 1 퐿 1 푚퐿 푚표푙  = ? 퐿 10−3푚퐿 1 푐푚3 푐푚3

______

0.087 푛푚 1 푚 1 푚푚  = ? 푚푚 1 10−9푛푚 103푚

______

7.874 푔 1 푘푔 (10−2푐푚)3 푘푔  = ? 푐푚3 10−3푔 (1 푚)3 푚3

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 -9 was 1.953 x 10 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? 14 Cd (νt = 9.86 x 10 Hz) 15 Co (νt = 1.21 x 10 Hz) 15 Cr (νt = 1.09 x 10 Hz) 14 Na (νt = 5.77 x 10 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.