Ch 221
Practice Exam #1
Name _________________________________
You must show all work (except the for the Metric-Metric conversions which you can simply
do by shifting a decimal place) and observe all significant figure conventions. Answers with
no work receive zero credit. You have 55 minutes to complete this exam, at which time you
must immediately stop work and hand in the exam to the instructor.
POINTS MADE
PART I: Calculations (39 pts)
PART II: Multiple Choice (36 pts)
PART III: Matching, etc (13 pts)
PART IV: Nomenclature (12 pts)
Total
Avogadro's number = 6.022 x 1023
PART I: Calculations
Atomic Mass. (10 pts). The element Si has 3 naturally occurring isotopes. From the
following table, and knowing how the atomic mass on the periodic table is calculated,
calculate the mass in amu's of the third isotope, 30Si. Hint: you'll need the atomic
weight of Si from the periodic table to solve for the mass of the isotope.
isotope
28
Si
29
Si
30
Si
mass (amu's)
27.97693
28.97649
% abundance
92.230
4.670 %
3.100 %
(10 pts) A man in a bar drinks a beer, little realizing that the ethanol molecules in it are
diffusing through the liquid at a rate of 1.24 m2/s. Calculate the rate of diffusion in
ft2/min. You MUST use 1 in = 2.54 cm (exact).
(10 pts) A piece of copper wire that is 10.0 cm long has a diameter of 3.0 mm. Copper
has a density of 8.92 g/cm3. How many atoms of copper are there in the piece of wire?
1. (12 pts) Draw all of the orbitals in the third shell of the hydrogen atom. Be sure to
include coordinate axes and labels.
2. (12 pts) Bohr Atom. What is the wavelength of the photon emitted when an electron in
the n = 6 energy level of hydrogen drops down to the n = 2 orbit?
Metric-Metric conversions (9 pts) – fill in the table.
25 mL =
L
kg =
1455 grams
35 m =
nm
PART II: Multiple Choice – Each question is worth 3 pts and there is only ONE
correct answer.
1. Which number has 4 significant figures?
(a) 4500
(b) 0.102
(c) 41.0072
(d) 0.009020
(e) 0.062
2. How many significant figures does the sum of the following contain?
(a) 1
(b) 2
(c) 3
(d) 4
8.5201 + 1.93
(e) 5
3. Which group of compounds are ALL ionic?
(a) H2O, NaCl, CS2
(d) H2O, FeCl3, CO2
(b) NaCl, CH4, CaCl2
(e) CaCl2, FeCl3, CO2
(c) CaCl2, FeCl3, NaCl
4. When a reaction of A and B is performed in a sealed vessel, no change in the mass is
observed. However, when the reaction is performed on the laboratory bench, the mass
after the reaction is greater than the mass before the reaction. Based on this
information, which of the following statements is true?
(a) Matter was created in the laboratory.
(b) An isotope of the reactant has been created.
(c) A gaseous product of the reaction was not weighed in the laboratory experiment.
(d) A gaseous reactant was not weighed in the laboratory experiment.
(e) Human error caused the discrepancies.
5. Which one of the following represents a physical change?
(a)
(b)
(c)
(d)
(e)
apples, when exposed to air, turn brown
bleach turns hair yellow
sugar, when heated, becomes brown
milk turns sour
water, when heated, forms steam
6. How many degrees Fahrenheit are there between -30.0 and 15.5 oC ?
(a) 81.9
(b) 107
information to tell
(c) 26.1
(d) 8.06
(e) not enough
7. Which of the following is an INCORRECT statement concerning cathode rays
associated with cathode ray tubes?
(a) they are repelled by a negatively charged plate (b) they travel in straight lines
(c) they are now known to be fast moving neutrons (d) they can be bent in a magnetic
field
8. After Rutherford observed that some alpha particles were scattered at large angles by
gold foil, he concluded that
(a) most of the mass of the atom is in the nucleus (b) the nucleus is positively charged
(c) the nucleus is very small
(d) the nucleus is very dense
(e) all of the above
9. What is the molecular weight (molar mass) of Fe(NO3)3?
(a) 117.9
(b) 186.0
(c) 85.9
(d) 6.022 x 1023
(e) 241.9
10. An isotope of which element is used as the standard for the relative mass scale for atoms?
(a) oxygen
(c) hydrogen
(b) carbon
(d) gold
11. Blackbody radiation and the photoelectric effect were explained by
(a) quantizing electromagnetic radiation as little massless particles or photons
(b) using classical physics concepts such as conservation of energy
(c) electrons occupy circular orbits
(d) Rutherford’s gold foil experiment
12. Complete this sentence: Atoms emit visible and ultraviolet light
(a) as electrons jump from lower energy levels to higher levels.
(b) as the atoms condense from a gas to a liquid.
(c) as electrons jump from higher energy levels to lower levels.
(d) as they are heated and the solid melts to form a liquid.
(e) as the electrons move about the atom within an orbit.
PART III: Matching, fill-in-the-blank (13 pts)
1. (4 pts total) Match the terms on the right with the definitions on the left. (1 pt each)
(a) _____ A concise statement of a relationship
between phenomenon that never changes
(b) _____ Tentative explanation for the behavior
of a system
1. fact
2. law
3. hypothesis
4. theory
(c) _____ Tentative model that has been repeatedly
verified by experiment
(d) _____ A valid observation about some
natural phenomenon
2. (4 pts total) For each example of matter on the left, choose the correct classification on
the right.
(a) _____ 2 substances present, 3 phases present 1. heterogeneous mixture
2. homogeneous mixture
(b) _____ 2 substances present, 1 phase present
3. compound
4. element
(c) _____ 1 substance present, 1 phase present,
substance cannot be decomposed by
chemical means
(d) _____ 1 substance present, 1 phase present,
substance can be decomposed by
chemical means
3. (5 pts total) Fill in the blank.
A mole of nitrogen atoms contains _______________ atoms.
A mole of nitrogen molecules contains _______________ molecules.
A mole of nitrogen molecules contains ________________ atoms.
A mole of nitrogen atoms has a mass of _______________ grams.
A mole of nitrogen molecules has a mass of _______________ grams.