Houston Community College System
Chemistry 1305
SAMPLE EXAM # 3
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HOUSTON COMMUNITY COLLEGE
CHEM 1305
Name: _________________________________
Exam # 3 (Chap. 8-10)
Score:
PART I – Multiple choice: (3 points each)
1) What is the term for the value corresponding to the number of atoms in 12.01 g of carbon?
A) Avogadro's number
B) atomic number
C) mass number
D) mole number
2) What is the number of magnesium atoms that equal a mass of 24.31 g?
A) 1
B) 12
C) 24
23
D) 6.02 × 10
3) Which of the following is equal to 1.00 mole of substance?
23
A) 6.02 × 10 sodium atoms, Na
23
B) 6.02 × 10 iodine molecules, I2
23
C) 6.02 × 10 sodium iodide formula units, NaI
D) all of the above
22
4) How many moles of argon gas contain 7.52 × 10 Ar atoms?
A) 0.0125 mol
B) 0.0801 mol
C) 0.125 mol
D) 0.801 mol
C) 102.16 g/mol
D) 113.11 g/mol
5) What is the molar mass of caffeine, C4H5N2O?
A) 43.03 g/mol
B) 97.11 g/mol
6) How many moles of chlorine gas react with 1 mol of hydrogen gas according to the balanced chemical
equation?
H2(g) + Cl2(g) → 2 HCl(g)
A) 1 mol
B) 2 mol
C) 3 mol
D) 4 mol
7) What term expresses the ratio of moles of reactants and products according to the coefficients in the balanced
chemical equation?
A) mole ratio
B) reactant ratio
C) product ratio
D) yield ratio
8) Which of the following expresses the amount of the actual yield compared to the theoretical yield?
A) experimental yield
B) percent yield
C) ratio yield
D) stoichiometric yield
9) In the following reaction, how many liters of water vapor, H2O, react to produce 1L of hydrogen gas?
C (s) + H2O (g)  CO (g) + H2 (g)
A) 1 L
B) 2 L
C) 3 L
2
D) 4 L
10) In an experiment, 1.201 g of charcoal reacts with 6.414 g of powdered sulfur. What is the mass of product?
C(s) + 2 S(s)  CS2(g)
A) 4.408 g
B) 5.213 g
C) 7.615 g
D) 8.816 g
11) What is the theoretical temperature at which the kinetic energy of a gas is zero?
A) absolute zero
B) -100°C
C) -273°F
D) -273 K
12) Which of the following states that the pressure and volume are inversely proportional for a gas at constant
temperature?
A) Boyle's law
B) Charles' law
C) Dalton's law
D) Gay-Lussac's law
13) If an aluminum scuba tank contains compressed air at 2750 psi, what is the pressure expressed in inches of
mercury? (760 mmHg = 14.7 psi, 1 inHg = 25.4 mmHg)
A) 92.0 inHg
B) 187 inHg
C) 5598 inHg
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D) 8.22 × 10 inHg
14) Which of the following changes decreases the pressure of a gas?
A) increasing the volume
C) decreasing the number of gas molecules
B) decreasing the temperature
D) all of the above
15) Which of the following represents the graph of volume versus temperature for a gas at constant pressure?
16) How many moles of Al2O3 are in 100 g of this substance?
A) 1.02 mol
B) 2.35 mol
C) 0.576 mol
D) 0.981 mol
17) What is the mass in grams of 1.25 mol of Na2SO4?
A) 0.00563 g
B) 114 g
C) 156 g
D) 178 g
18) How many hydrogen atoms are in 50.0 g of H2O?
A) 1.67 X 1024 atoms
C) 3.34 X 1024 atoms
B) 2.77 atoms
D) 5.54 atoms
19) What is the percent by mass of oxygen in acetic acid, HC2H3O2?
A) 22.6%
B) 53.3%
C) 65.7%
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D) 49.4%
20) A compound is 47.3% Cu and 52.7% Cl by mass. What is the empirical formula of this compound?
A) CuCl
B) CuCl3
C) CuCl2
D) Cu2Cl
PART II – Show All Your Work: (8 points each)
1) What is the density of ozone gas, O3, at STP?
2) What is the mass of potassium iodide (166.00 g/mol) that yields 0.500 g of lead (II) iodide (461.0 g/mol)
precipitate?
__Pb(NO3)2(aq) + __KI(s) → __PbI2(s) + __KNO3(aq)
3) What is the volume of oxygen gas at STP from the decomposition of 10.8 g of mercuric oxide
(216.59 g/mol)?
__HgO(s) → __Hg(l) + __O2(g)
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4) If 50.0 cm of xenon gas is at 0.460 atm and -123°C, what is the volume at STP?
5) An organic compound has the empirical formula C2H3O and a molar mass of 172.2 g/mol. What is the
molecular formula of this compound?
6) BONUS QUESTION – Show All Your Work: (10 points)
How many liters of H2 gas at STP will be formed from the reaction of 10.0 grams of aluminum metal with excess
hydrochloric acid?
2 Al (s) + 6 HCl (aq) → 2 AlCl3 (aq) + 3 H2 (g)
4
5
Answer Key
Part I - Multiple Choice
1) A
8) B
15) D
2) D
9) A
16) D
3) D
10) C
17) D
4) C
11) A
18) C
5) B
12) A
19) B
Part II - Show Your Work
1) 2.14 g/L
2) 0.360 g
3) 0.558 L
4) 41.9 cm
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5) C8H12O4
6) 12.5 L
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6) A
13) C
20) C
7) A
14) D