Chem 120
Fritsch
Ch 1 -3 Practice Problems
The following problems are intended to provide you with additional practice in preparing for
the exam. Questions come from the textbook, previous quizzes, previous exams, and other
sources. Solutions are supplied in a separate document.
1. The Earth has an average density of 5.52 g/cm3. Report this density in kg/m3 and lb/ft3.
2. Fill in the table with the correct name or molecular formula.
Formula
Name
Sulfur trioxide
Lithium phosphate
Cu(NO3)2
N2Cl4
H2SO4
3. Determine the oxidation state for the requested element in each of the following.
KNO2
Na2S
Cr3(PO4)3(SO4)(Cl)
Ca(OH)2
oxidation state of N =
oxidation state of S =
oxidation state of Cr =
oxidation state of Ca =
4. The Pepperdine pool is 50 m long, 25 m wide, with an average depth of 6.78 ft. What mass
of water (in kilograms) does the pool contain?
5. Place an X in the appropriate column corresponding the isotopes and element symbols given.
Symbol
# of protons <
# of protons <
# of protons >
# of neutrons =
# of neutrons
# of electrons
# of electrons
# of electrons
57
Mn4+
37
Cl-
14
N
S
34 2-
Chem 120
Fritsch
6. Which of the following pairs of elements will form anions with the same charge in ionic solids?
Na and Cs
Mg and S
F and Cl
Rb and Sr
Br and O
7. In Faraday’s experiment with the cathode ray tube, the path of the electrons inside the tube was the
result of which properties?
I. mass of the
electron
II. volume of the
electron
III. charge on the
electron
IV. force of the
magnetic field
8. The water in the Pacific Ocean contains a number of dissolved cations (magnesium, sodium,
calcium, and potassium) and anions (chloride and sulfate). Each kilogram of Pacific Ocean
water contains 1,153 mg of magnesium, 412 mg of calcium, and 19,432 mg of chloride. What is
the percent mass of magnesium in the water? What is the mass percent of chloride in the
water? If you had, 0.578 kg of ocean water, how many calcium ions would it contain?
9. In the General Chemistry lab, you and your lab partners are measuring the masses of pennies to see
how they differ. Unfortunately, you measured the masses to different levels of precision with the
following measurements: 2.1625 g, 2.043 g, 2.03 g. What is the sum of the masses of the pennies with
the appropriate number of significant figures?
10a. Which of these Cu(s), O2(g), H2O(l), N2(g), and He(g) has the highest density (g/mL)?
10b. Which of the following pairs of molecular formulas have the same empirical formula?
N2O4
and
NO2
H2O
and
H2O2
H3PO4
and
H3PO3
C2H6O
and
C6H12O6
Chem 120
Fritsch
11. Combustion analysis was completed on a 0.534 g sample of 1,2-Bis-(4-pyridylthio)propane
(molecular formula = C13H14N2S2) in the presence of excess oxygen. Determine the mass (in
grams) of the carbon dioxide and nitrogen dioxide that were collected.
12. Hemoglobin is 8.0% heme (C34H32FeN4O4) by mass. A crime scene technician collects a
blood sample that contains 0.62 g of hemoglobin. How many Fe atoms are contained in the
sample?
13. Mass spectrometry is a highly accurate technique
used to determine the mass of ions and molecules. A
sample of silicon was placed into the mass
spectrometer, and three isotopes were observed.
Unfortunately, your lab partner only recorded the
observed masses and isotope abundances given in the
table at the right. Determine the mass of the third
isotope to the same number of significant figures as
those data and give the appropriate symbol for this
isotope.
Silicon
isotope
Atomic
mass (u)
% natural
abundance
28
27.9769
92.23
30
29.9738
3.10
Si
Si
14. Ferrocene is a famous compound from inorganic chemistry because it was the first to
contain a Fe-C bond. A 0.9437 g sample of ferrocene (containing only C, H, and Fe) was
submitted to combustion analysis which yielded 2.233 g CO2 and 0.457 g H2O. Determine the
empirical formula of ferrocene.
15. Alum (KAl(SO4)2•12H2O) is a useful food preservative and is prepared from aluminum and
other chemicals. How many moles of potassium are in 649 g of alum? What is the percent
mass of sulfur in alum? What mass of alum (in grams) can be prepared from 13.2 kg of
aluminum?
16. What is the number of chloride ions in 1.235 L of a 6.4 % by mass solution of magnesium
chloride in water? (density = 1.037 g/mL)
17. Ernest Rutherford proposed his model of the nucleus based on his experiments with a thin
gold foil and a radioactive  particle emitter. Which of the following (ions, atoms, isotopes)
would have given the same results as observed by Rutherford’s original experiments.
6 +
16
27 3+
Li
ClO2
H+
Al
Chem 120
Fritsch
18. If the elemental analysis for a compound indicates that it was 50 % carbon by mass and 50 %
hydrogen by mass, which of the following statements is true?
A.
B.
C.
D.
There are more hydrogen atoms than carbon atoms in the empirical formula.
There are more carbon atoms than hydrogen atoms in the empirical formula.
There are the same number of hydrogen and carbon atoms in the empirical formula.
The empirical formula cannot be determined from this information.
Answer:_____ _____
19. Propane (C3H8) is sold in metal containers for use as fuel for barbeques or camp stoves. You
purchased a camp stove bottle and it had an initial mass of 1.568 kg. After much use, you
measured the mass of the empty container and found it to be 0.983 kg. How many moles of
propane were in the bottle? How many carbon atoms were in the bottle? How many grams of
hydrogen were in the bottle?
20. Calculate the following quantities:
a) the mass in grams of 0.53 moles of manganese (II) sulfate
b) the number of moles of iron(III) perchlorate in a 63.8 g sample
c) the number of nitrogen atoms in a 21.6 g sample of ammonium nitrite.
21. In geology class, you study a 68.74 g rock that is 7.86% by mass fayalite (Fe2SiO4), 13.56% by
mass forsterite (Mg2SiO4), and the balance is made up of silicon dioxide. What is the mass
percentage of silicon in the rock? How many moles of iron are in the rock?
22. How many oxygen atoms are in each molecule of aluminum sulfate?
How many hydrogen atoms are in each molecule of ammonium phosphate?
How many oxygen atoms are in each molecule of copper(I) carbonate pentahydrate?
Chem 120
Fritsch
23. Fill in the missing name for the compound or chemical formula.
name
Chemical formula
tin(IV) chloride
iron(III) bromide
ammonium perchlorate
Cobalt(II) oxide
Potassium nitrate
BaSO4
Li2SO3
Mg3(PO4)2
(NH4)2SO4
Na2CO3
24. Calcium and iodine can combine to form an ionic compound. How many iodide ions would
be required to combine with 3.6 x 1022 calcium ions?
25. Calculate the atomic mass of Magnesium from the mass of its isotopes and the percent
natural abundance for each isotope.
Isotope
Isotope mass (amu) % natural abundance
24
Mg
23.9850
78.99
25
Mg
24.9858
10.00
26
Mg
25.9826
11.01
26. Consider a rigid, ball with a mass of 0.1034 g and a volume of 468.0 L. Air has a density of
1.176 g/L and if the density of the ball is less than the density of air, the ball will float.
a. All of the contents of the ball are removed by a vacuum. Will the ball float?
b. The ball is filled with carbon dioxide with a density of 1.761 g/L. Will the ball float?
c. The ball is filled with helium with a density of 0.113 g/L. Will the ball float?
27. Of the following pairs which have the same number of protons, neutrons, electrons.
3
H and 3He
14
C and 15N
19
F and 18F
Chem 120
Fritsch
28. Brass is an alloy of copper and zinc and the color of brass can be adjusted by varying the
percent mass of each element in the alloy. A particular alloy contains 24.65% zinc by mass with
the remainder made up by copper. To make 239.5 g of this alloy, how much copper would be
required? For another sample of the alloy, 72.2 g of copper was combined with what mass of
zinc in grams?
29. An average dorm room at Pepperdine measures 14 ft wide, 18 ft long, and 8 ft high. The
heating and air conditioning system is able to replace all the air in the room at a rate of 1432
L/min. How long would it take to replace all the air in the room?
30. In the General Chemistry lab, you collect the weight of an empty test tube and find it to be
37.952g. You fill the test tube to the top with mercury (density = 13.53 g/mL) and collect the
mass on a balance and find it to be 217.903g. You empty the test tube and fill it to the top with
water. What is the mass would the balance read now?