Houston Community College System
Chemistry 1405
SAMPLE EXAM # 3
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HOUSTON COMMUNITY COLLEGE
CHEM 1405
Name: _____________________
Exam # 3 (Chap. 8-12)
Score:
PART I – Multiple choice: (3 points each)
1)
How many moles of chlorine gas react with 1 mol of hydrogen gas according to the following balanced
chemical equation?
H2(g) + Cl2(g) → 2 HCl(g)
A) 1 mol
2)
B) 2 mol
C) 3 mol
D) 4 mol
In the following reaction, if 4 moles of sulfur is used how many moles of oxygen is required?
S
A) 1 mole
+
B) 2 moles
O2
→
SO3
C) 3 moles
D) 4 moles
E) 6 moles
3)
What is the correct statement of the following reaction if 10 g of nitrogen and 10g of Hydrogen were
used?
N2 +
4)
H2 →
NH3
A) Hydrogen is limiting reactant
B) Hydrogen is excess reagent
C) Nitrogen is limiting reactant
D) Nitrogen is excess reagent
E) B and C
In the following reaction, theoretically, 50g of CuS was produced. Calculate the mass of Copper and
Sulfur to be used.
Cu +
S →
CuS
A) 33.24g Cu and 16.77g S
B) 30g Cu and 20g H
D) 42.60g Cu and 7.40 g S
E) 25g Cu and 25g S
C) 35.0g Cu and 15g H
5) What is the % yield if 45.6g of CuS was produced in the above reaction?
A) 87.9%
6)
B) 97.8%
C) 91.2%
D) 95.6%
E) None of them
If the air pressure in this room is 785 mmHg, what is the pressure in inchHg (760 mmHg = 29.9 inchHg)?
A) 30.2 inchHg
B) 30.88 inchHg
C) 24.9 inchHg
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D) 36. 2 inchHg
E) None of them
7)
Calculate the amount of 2.7 L Neon under STP conditions
A) 0.12 moles
B) 1.6 moles
C) 1.9 moles
D) 2.3 moles
E) None of them
8) According to ideal gas equation what is the volume of 1mole gas under STP conditions?
A) 18.8 L
B) 22.4 L
C) 27.3 L
D) 30.8 L
E) 44.01 L
9) 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
10) 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
11) Assuming STP conditions, how many liters of water vapor, H2O react to produce 1L of hydrogen gas?
C(s) + H2O(g)  CO(g) + H2(g)
A) 8.1 10-4 L
B) 2.2 x 10-3 L
C) 3.1 x 10-2 L
D) 0.44 L
12) 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
E) None of them
13) Calculate the mass of Fe2O3 produced with 20g Iron(II) oxide and 20g of oxygen in the following reaction
FeO
A) 20g
+

O2
B) 45.2g
Fe2O3
C) 93.5g
D) 59.6g
E) 22.2g
14) Which of the following states that the temperature and volume are directly proportional for a gas at constant
pressure?
A) Boyle's law
B) Charles' law
C) Dalton's law
D) Gay-Lussac's law
15) If an aluminum scuba tank contains compressed air at 2750 psi, what is the pressure expressed in inches of
mercury?
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A) 92.0 inHg
B) 187 inHg
C) 5594 inHg
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D) 8.22 × 10 inHg
16) Identify the molecular solids among MgCl2, Fe, SiO2, and He
A) SiO2
B) MgCl2
C) He
D) Fe
17) A 1L Neon gas at constant pressure is cooled from 50 oC to 25 oC. What is the final volume?
A) 0.5 L
B) 0.7 L
C) 0.9 L
D) 1.2 L
E) 1.5 L
18) In which of the following the atoms are held together by ionic bonds?
A) AlCl3
B) Mg3N2
C) Cu2S
D) all of the above
19) How many bonding electrons are present in CO2 molecule?
A) 2
B) 4
C) 6
D) 8
E) 10
20) What is the molecular geometry of SO2
A) Linear
C) Trigonal planar
B) Bent
D) Trigonal pyramidal
E) Tetrahedron
PART II – Show All Your Work: (8 points each)
1) Calculate the mass of NH3 and limiting reactant in the reaction of 25g of Hydrogen and 25g of Nitrogen in
the following reaction.
N2
+
H2
→
NH3
2) What is the mass of potassium iodide that yields 0.500 g of lead (II) iodide?
__Pb(NO3)2(aq) + __KI(s) → __PbI2(s) + __KNO3(aq)
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3) What is the volume of oxygen gas at STP from the decomposition of 10.8 g of mercuric oxide
( molar mass of HgO: 216.59 g/mol)?
__HgO(s) → __Hg(l) + __O2(g)
4) Write the Lewis dot structure of NH3 and indicate molecular geometry
5) Hydrogen has an electronegativity value of 2.1. Given the electronegativity of N, O, and P (3.0, 3.5, and 2.1,
respectively), predict which of the following has nonpolar bonds.
NH3, H2O, PH3
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BONUS QUESTION – Show All Your Work: (10 points)
Draw the Lewis structure for the following molecules and indicate the number of bonding electrons, nonbonding electrons and the shape of each one.
SiO2, CH4
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