CHEM 3: Midterm Exam 2: Summer 2015
Name:________________________________________
INSTRUCTIONS: On the front AND back of the scantron, fill out your name and 7-digit student ID. Fill in
this information from left to right in the provided fields, and BUBBLE IN the values on the scantron. 1
point will be deducted from your exam grade for incomplete or erroneous filling of the scantron.
Please read each question carefully. Where the question specifies “MARK ALL THAT APPLY”, you MIGHT
need to select more than one answer on the scantron.
1.
MARK ALL THAT APPLY: Select ALL of the formulas below which are reasonable EMPIRICAL formulas.
A. N(NO2)3
(Trinitramide, a rocket propellant oxidizer)
B. CH2ClCHCHCl
(Dichloropropene, a fumigant used in farming)
C. CH3NHNH2
(Monomethylhydrazine, a rocket fuel)
D. CH2CHCCH3(C3H5)2
(Syntin, a rocket fuel)
E. None of the above are reasonable empirical formulas.
2.
NASA’s Green Propellant Infusion Mission of 2016 will test the substance hydroxylammonium nitrate as a new, more
environmentally friendly rocket propellant. If the MOLECULAR formula of hydroxylammonium nitrate is NH3OHNO3, what is
the corresponding EMPIRICAL formula?
A. In this case the empirical formula is equal to the molecular formula: N2H3O4
B. N2H4O4
C. NHO
D. NH2O2
E. N3H4O3
3.
The substance trimethyl isocyanurate has a molar mass of 171.13 g/mol with an EMPIRICAL formula of C2H3NO. What is the
MOLECULAR formula of this substance?
A. In this case, the empirical formula is equal to the molecular formula: C2H3NO
B. C4H6N2O2
C. C6H9N3O3
D. C9H12N3O3
E. None of the above.
4.
Surfuryl fluoride, a structural fumigant and insecticide commonly used to control drywood termites, is composed of 31.37%
sulfur, 31.37% oxygen, 37.26% fluorine by mass. Based on this elemental composition, what is the EMPIRICAL formula of
surfuryl fluoride?
A. SOF
B. S3O3F4
C. SO2F2
D. SOF2
E. Cannot determine from this information: mass spectrometry data would have to be provided.
For questions # 5-12, categorize each reaction as one the 5 possibilities below:
A.) Synthesis
B.) Double Replacement
C.) Combustion
D.) Decomposition
E.) Single Replacement.
Each reaction only fits one category, but one category may appear more than once.
5.
2 NH4ClO4 → N2 + Cl2 + 4 H2O + 2 O2
6.
2 AuCl3 + 3 Mg → 2 Au + 3 MgCl2
7.
S8 + 24 F2 → 8 SF6
8.
4 C6H5NH2 + 31 O2 → 2 N2 + 24 CO2 + 14 H2O
9.
2 CO2 + 2 CH3CH2OH → C6H12O6
10. 2 KClO3 → 2 KCl + 3 O2
11. U + 2 ClF3 → UF6 + Cl2
12. Ba(NO3)2 + H2SO4 → BaSO4 + 2 HNO3
13. MARK ALL THAT APPLY: Mark any reactions below that are not properly balanced.
A. 2 Al + Fe2O3 → Al2O3 + 2 Fe
(thermite reaction)
B. C12H22O11 + H2O → 4 CO2 + 4 CH3CH2OH
(maltose fermentation by yeast to make beer)
C.
(used in catalytic decomposition rocket engines)
3 N2H4 → 4 NH3 + N2
D. 6 CO2 + 6 H2O → C6H12O6 + 9 O2
E.
(chemical conversion involved in photosynthesis)
None of the above: ALL of these reactions are balanced.
14. In the equation below, what should the coefficient be on the aluminum atoms (Al) when properly balanced with the
smallest whole number coefficients?
____ Al + ____ Mn2O7 → ____ Mn + ____Al2O3
A.
B.
C.
D.
E.
2
3
7
9
14
15. If the reaction below was balanced properly with the smallest whole number coefficients, what would be the stoichiometric
coefficient in front of the diatomic oxygen (O2)?
2 C8H18O2 + ____ O2 → 16 CO2 + 18 H2O
A.
B.
C.
D.
E.
15
16
17
23
25
16. In the industrial smelting process to convert ores to metals, the reaction below is utilized to transform malachite (a
naturally occurring mineral of copper) to elemental, metallic copper. When properly balanced with the smallest whole
number coefficients, what would be the stoichiometric coefficient in front of the carbon dioxide?
_____ Cu2CO3(OH)2 + ____ C → ____ Cu + ____ CO2 + ____ H2O
A.
B.
C.
D.
E.
1
2
3
4
6
17. When the reaction below is properly balanced with the smallest whole number coefficients, what is the stoichiometric
coefficient in front of the ammonium nitrate?
____ Co(NO3)2 + ____ (NH4)3PO4 → ____ Co3(PO4)2 + _____ NH4NO3
A.
B.
C.
D.
E.
1
2
3
6
9
18. MARK ALL THAT APPLY: Select ALL of the ionic compounds below that would form INSOLUBLE precipitates in water.
A. Al2(SO4)3
B. Pb(OH)2
C. FeCO3
D. K3PO4
E. None of substances above would be insoluble in water.
19. If AgNO3(aq) was mixed with (NH4)2CrO4(aq), what is one possible product from this double replacement reaction?
A. AgCrO4
B. (NH4)2NO3
C. AgNH4
D. (NO3)2CrO4
E. Ag2CrO4
20. How many moles of oxygen gas would be needed to react with 30.0 moles of iron metal according to the equation below?
4 Fe(s) + 3 O2(g) → 2 Fe2O3(s)
A. 15.0 moles
B. 22.5 moles
C. 30.0 moles
D. 40.0 moles
E. 45.0 moles
21. Considering the reaction below, how many moles of magnesium metal would be needed to produce 60.0 moles of
magnesium phosphide?
6 Mg(s) + P4(s) → 2 Mg3P2(s)
A. 10.0 moles
B. 20.0 moles
C. 120 moles
D. 180. moles
E. 360. moles
22. Considering the reaction below, how many grams of oxygen gas (O2) could be generate starting from 2.00 moles of
Fe2(Cr2O7)3?
Fe2(Cr2O7)3 → 3 Cr2O3 + 2 Fe + 6 O2
Molar Masses (g/mol):
759.65
151.99
32.00
A. 10.7 g
B. 384 g
C. 1520 g
D. 115.8 g
E. 292,000 g
23. What mass of water would be needed to fully react with 10.0 grams of tetraphosphorus decoxide according to the reaction
below?
P4O10 + 6 H2O → 4 H3PO4
Molar Masses (g/mol): 283.9 18.02
97.99
A.
B.
C.
D.
E.
0.863 g
13.8 g
40.0 g
116 g
3920 g
24. What is the LIMITING reagent, if 12.0 moles of calcium hydroxide, 4.50 moles of tetraphosphorus decoxide, and 144 g of
water are mixed together and react according to the equation below?
2 Ca(OH)2 + P4O10 + 2 H2O → 2 Ca(H2PO4)2
A.
B.
C.
D.
E.
Ca(OH)2
P4O10
H2O
Ca(H2PO4)2
There would be no limiting reagent starting from this mixture.
25. Syngas is produced from methane (CH4) and water according to the reaction below. What is the limiting reagent, if 45.0 g
of methane is mixed with 48.7 g of water?
CH4 + H2O → CO + 3 H2
Molar masses (g/mol):
16.04 18.02 28.01 2.016
A. CH4 is the limiting reagent because there are only 45.0 grams of it, while there are 3.7 more grams of water available
B. H2O is the limiting reagent because there are few moles of this substance even though there is a larger mass
C. CO is the limiting reagent because it has the largest molar mass and therefore the fewest number of moles
D. H2 is the limiting reagent because it has the lowest molar mass and would be consumed first in the reaction
E. Cannot determine the limiting reagent from the information provided: the densities would have to be provided.
26. If 20.8 g of phosphorus pentachloride react with an EXCESS of diphosphorus pentaoxide according to the reaction below,
but only 15.3 g of POCl3 is obtained as the final product, what is the percent yield?
3 PCl5 +
Molar Masses (g/mol):
A.
B.
C.
D.
E.
6.66%
10.0%
44.1%
59.9%
166%
208.22
P2O5 →
141.94
5 POCl3
153.32
FREE RESPONSE: Show your work for full credit. Partial credit will be assigned.
1.
The major component of coconut oil is the saturated fat, CH2CHCH2(C12H24O2)3. Write the balanced chemical equation for
the complete combustion of this saturated fat. Write the phases for each component is not necessary.
2.
Predict the products and balance the chemical equation for uranium (VI) fluoride reacting with magnesium metal. Write
the phases for each component is not necessary.
3.
Consider the two experimental observations below:
Reaction 1: AgClO3(aq) + Fe(NO2)3(aq) → Generates a PRECIPITATE.
Reaction 2: AgClO3(aq) + Fe(NO3)3(aq) → Does NOT generate a precipitate.
Based on this information, write the balanced chemical equation for the precipitation in reaction 1. BE SURE TO INDICATE THE
PHASES OF THE PRODUCTS and specify the component that is responsible for the formation of the precipitate.
4.
In the depths of space, when even starlight can’t be relied on, spacecraft need some form of long-lasting energy to endure
potential decades without recharging. For a possible mission to Venus, NASA has proposed using lithium as a rocket fuel and
the planet’s carbon dioxide rich atmosphere as an oxidizer to react according to the equation below:
4 Li + CO2 → 2 Li2O + C
How many kilograms of carbon dioxide would be needed to react with 1500 kg of lithium metal?
EXTRA CREDIT: (10 points) Show your work for credit; no partial credit will be awarded.
A mixture of dinitrogen tetroxide and hydrazine reacts explosively according to the equation below and is used to power military,
orbital and deep space rockets.
N2O4(l) + 2 N2H4(l) → 3 N2(g) + 4 H2O(g)
Consider a rocket designed to hold a maximum of 7.000 x 103 gallons of this dinitrogen tetroxide / hydrazine mixture. Using this
maximum volume of the rocket tanks, calculate the mass (in tons) of each reactant needed to maximize the energy released in this
reaction by minimizing the amount of each unreacted reagent left after complete conversion to the products.
Reference Information:
Density of dinitrogen tetroxide = 1.448 g/cm3
Density of hydrazine = 1.020 g/cm3
1 gallon = 3.78541 L
1 ton = 2000 pounds
1 pound = 453.592 g
Mass of N2O4 = ______________________________________________
Mass of N2H4 = ______________________________________________