Practice Exam #3 with Answers

CH1410 Practice Exam #3 (Katz) Sp2015
Section 1 - Multiple Choice - Write the letter of the BEST CHOICE in the space provided. C
_____ 1. How many moles of H2 can be made from the complete reaction of 3.0 moles of Al?
Reaction: 2 Al + 6 HCl → 2 AlCl3 + 3 H2
A) 3 moles
B) 3.0 moles
C) 4.5 moles
D) 9.0 moles
3.0 mol Al x
3 mol H2
2 mol Al
= 4.5 mol H2
D
_____ 2. How many moles of sodium metal are needed to make 3.6 moles of sodium chloride?
Reaction: 2Na + Cl2 → 2NaCl
A) 0.9
B) 7.2
C) 1.8
D) 3.6
3.6 mol NaCl x
2 mol Na
= 3.6 mol Na
2 mol NaCl
B
_____3. The theoretical yield of a reaction is 75.0 grams of product and the actual yield is 42.0g. What
is the percent yield?
A) 75.0
42 g
B) 56.0
x
= 56%
C) 31.5
75 g
D) 178
D
_____ 4. Given the balanced equation CO2 + Si → SiO2 + C, if you were to react 1 mole of CO2 with
1 mole of Si, which statement is TRUE?
A) The CO2 is the limiting reactant.
B) The Si is the limiting reactant.
C) The SiO2 is the limiting reactant. D) You have equal stoichiometric amounts of reactants.
B
_____ 5. Consider the following reaction: 2 Mg + O2 → 2 MgO , △H rxn = -1203 kJ
Calculate the amount of heat (in kJ) associated with complete reaction of 4 moles of Mg.
A) -1203 kJ
B) -2406 kJ
C) -601.5 kJ
D) -4812 kJ
4 mol Mg x
-1203 kJ
2 mol Mg
= -2406 kJ
D
_____ 6. Which Lewis structure below correctly represents the compound formed between magnesium
and sulfur?
A)
C)
Mg+
S
S
-
-
Mg2+
S
-
B)
Mg+
S
D)
Mg2+
S
2-
Mg+
2-
C
_____ 7. Lewis theory predicts that the formula for an ionic compound of fluorine and calcium is:
A) CaF
B) Ca2F
C) CaF2
D) CaF3
D
_____ 8. When a nonmetal bonds with a nonmetal
A) a molecular compound forms.
B) a covalent bond is involved.
C) electrons are shared.
D) all of the above are true
A
_____ 9. What is the correct Lewis structure for Br2?
A)
B)
Br
Br
Br
Br
C)
Br
Br
D) Br
Br
D
_____10. The total number of electrons to be counted for the Lewis structure of the SO3 molecule is
A) 4
O
B) 8
C) 18
D) 24
S
O
O
N
A
_____11. The Lewis structure,
A) NO2+
B) NO2-
O
O
represents
C) NO2
D) both NO2+ and NO2-
A
_____12. Lewis theory predicts that the formula for an ionic compound of barium and sulfur is:
A) BaS
B) Ba2S
C) BaS2
D) BaS3
C
_____13. The central chlorine atom in the chlorate anion, ClO3- is surrounded by
O
A) two bonding pairs and two unshared pairs of electrons.
B) one bonding pair and three unshared pairs of electrons.
C) three bonding pairs and one unshared pair of electrons.
D) two double bonds and no unshared pairs of electrons.
Cl
O
D
____ 14. Which of the following compounds has resonance structures?
A) CH4
B) H2O
C) NH3
D) O3
O
O
O
O
O
O
C
_____15. What is the angle between electron groups in the trigonal planar electron geometry?
A) 90°
B) 109.5°
C) 120°
D) 180°
C
_____ 16. What is the electron geometry if you have 4 electron groups around the center atom?
A) linear
B) trigonal planar
C) tetrahedral
D) trigonal bipyramidal
O
A
_____ 17. What is the molecular geometry if you have a double bond, a single bond and 1 lone pair
around the central atom?
A) bent
B) linear
C) tetrahedral
D) trigonal pyramidal
S
O
O
A
_____18. The elements with the highest electronegativity values tend to be found in the:
A) upper right-side of the periodic table.
B) lower right-side of the periodic table.
C) upper left-side of the periodic table.
D) lower left-side of the periodic table.
B
_____19. Which molecule listed below has a polar covalent bond?
A) NaCl
B) H2O
C) H2
D) all of the compounds
D
_____20. Which molecule listed below is a nonpolar molecule?
A) CCl4
B) CO2
C) BH3
D) all of the compounds
A
_____21. How many kilojoules of heat are needed to completely vaporize 24.40 grams of water at its
boiling point?
For water, ΔHvap = 40.60 kJ/mol
A) 55.04
B) 550.0
C) 29.98
D) 300.0
24.40 g H2O x
1 mol H2O x 46.60 kJ
18.00 g H2O 1 mol H2O
= 55.04 kJ
C
_____22. Compare a small pot of water that is boiling vigorously to a large pot of water that is boiling
gently. Which statement is TRUE?
A) The small pot is boiling at higher temperature than the large pot.
B) The large pot is boiling at a higher temperature than the small pot.
C) Both pots are boiling at the same temperature.
D) The vapor pressure of the liquid is lower than the pressure above the pot in each case. D
_____23. How much energy does it take to melt a 16.87 g ice cube? For water, ΔHfus = 6.02 kJ/mol
A
A) 102 kJ
B) 108 kJ
C) 936 J
D) 5.64 kJ
16.87 g H2O x
1 mol H2O x 6.02 kJ
18.00 g H2O 1 mol H2O
= 5.64 kJ
_____24. Which intermolecular force is due to the formation of an temporary dipole?
A) dispersion forces
B) dipole-dipole forces
C) hydrogen bonding
D) none of the above
D
_____25. Which molecule below has hydrogen bonding capability?
A) CH4
B) HCl
D) CH3CH2OH
C) H2
B
_____26. Name the following alkane:
A) 1,3-dimethylhexane
CH3
B) 4-methylheptane
CH2 CH2 CH CH2 CH2 CH3
C) 2-propylpentane
D) 1-methyl-1-propylbutane
CH3
A
_____27. Which of the following alkanes is 1,4,-dichloropentane?
A)
CH3 CH CH2 CH2 CH2
Cl
B)
CH2 CH2 CH2 CH2
Cl
Cl
Cl
C)
CH3 C
CH2 CH2 CH3
Cl
Cl
D)
Cl
CH3 CH CH2 CH CH3
Cl
C
_____28. Name the major functional group in the following compound:
A) alcohol
B) aldehyde
C) ketone
D) carboxylic acid
O
CH3 CH2 C CH3
Section 2 - Answer the following computational questions using the information provided. You
must show a plan for your calculations, along with the conversion factors involved for full credit .
Write your answer in the box provided. 1. What is the limiting reactant for the reaction below given that you start with
2.50 grams of C and 2.50 grams of SiO2? (Molar masses: C, 12.01; SiO2, 60.09)
Reaction: C + SiO2 → SiC + O2
2.50 g C x
1 mol C x 1 mol O2
12.01 g C
1 mol C
2.50 g SiO2 x
1 mol SiO2 x 1 mol O2
= 0.0416 mol O2
60.09 g SiO2 1 mol SiO2
limiting
reagent
= 0.208 mol O2
theoretical
yield
2. How many moles of NH3 can theoretically be produced by the reaction of
2.00 g of N2 with 3.00 g H2? (Molar masses: N2, 28.02; H2, 2.02)
Reaction: N2(g) + 3 H2(g) → 2 NH3(g)
3.00 g H2 x
1 mol H2 x 2 mol NH3
2.02 g H2
3 mol H2
= 0.990 mol NH3
2.00 g N2 x
1 mol N2 x 2 mol NH3
28.02 g N2
1 mol N2
= 0.143 mol NH3
limiting
reagent
theoretical
yield
3. In the following reaction, if you start with 42.0 g of CO2 and 99.9 g KOH, which is the limiting reactant? (Molar masses: CO2, 44.01; KOH, 56.11)
Reaction: CO2 + 2KOH → K2CO3 + H2O
42.0
g CO2 x
1 mol CO2 x 1 mol H2O
44.01 g CO2 1 mol CO2
= 0.954 mol H2O
99.9 g KOH x
1 mol KOH x 1 mol H2O
56.11 g KOH 2 mol KOH
limiting
reagent
= 0.890 mol H2O
theoretical
yield
4. If you start with 15.5 g of Na2S and 12.1 g CuSO4 and produce only 3.05 g of CuS, what is the percent yield of CuS for the following reaction? (Molar masses: Na2S, 78.05; CuS, 95.62;
CuSO4, 157.62)
Reaction: Na2S + CuSO4 → Na2SO4 + CuS
15.5 g Na2S x
1 mol Na2S
1 mol CuS
x
x
78.05 g Na2S 1 mol Na2S
12.1 g CuSO4 x
95.62 g CuS
= 18.9 g CuS
1 mol CuS
1 mol CuSO4
1 mol CuS
95.62 g CuS
x
x
= 7.34 g CuS
157.62 g CuSO4 1 mol CuSO4
1 mol CuS
theoretical
yield
limiting
reagent
3.05 g
x 100%
7.34 g
= 41.5%