CHEM 2: Midterm Exam 2: Fall 2013 (100 points)
Name:________________________________________
Please read each question carefully. Where the question specifies “MARK ALL THAT APPLY”, you may select more
than one answer on the scantron.
1.
Select a 3p orbital below.
A.
B.
C.
2.
What is the electron configuration for Sulfur (S)?
A. 1s21p61d8
B. 1s22s22p63s6
C. 1s22s22p62d6
D. 1s22s22p63s23p4
E. None of the above.
3.
What is the electron configuration for nitride, N3-?
A. 1s22s1
B. 1s22s22p1
C. 1s22s22p3
D. 1s22s22p6
E. 1s22s22p63s23p1
4.
How many VALENCE electrons does a neutral Phosphorus atom have?
A. 15
B. 10
C. 8
D. 5
E. None, they are all core electrons.
5.
How many CORE electrons does a neutral Calcium atom have?
A. 20
B. 18
C. 10
D. 8
E. 2
6.
How many total electrons can fit into the entire 3d subshell?
A. 20
B. 14
C. 10
D. 6
E. 2
D.
E.
For questions # 7-13, categorize each reaction as:
A.) Synthesis
B.) Double Replacement
C.) Combustion
D.) Decomposition
There may be more than one of each category.
7.
Na3PO4 + 3 RbI → 3 NaI + Rb3PO4
8.
8 Fe2S3 → 16 Fe + 3 S8
9.
Cu(s) + 2 AgNO3(aq) → Cu(NO3)2(aq) + 2 Ag(s)
10.
2 K + 2 H2O → 2 KOH(aq) + H2
11.
2 Al + 3 Cl2 → 2 AlCl3
12.
C12H22O11 + 12 O2 → 12 CO2 + 11 H2O
13.
CaO + CO2 → CaCO3
E.) Single Replacement.
14. Circle ANY formula below which is a reasonable EMPIRICAL formula.
A. C6H12N2
B. C12H22O11
C. C6H6O6
D. All of the above are reasonable empirical formulas.
E. None of the above are reasonable empirical formulas.
15. Circle ANY formula below which could be a possible MOLECULAR formula.
A. C6H12N2
B. C12H22O11
C. C6H6O6
D. ALL OF THE ABOVE are possible MOLECULAR formulas.
E. ONLY A & C are reasonable MOLECULAR formulas.
16. The MOLECULAR formula of bromotrichlorobenzene is C6H2BrCl3. What is the corresponding EMPIRICAL formula for
bromotrichlorobenzene?
A. C12H4Br2Cl6
B. C3HBrCl2
C. CHBrCl
D. In this case, the molecular formula equals the empirical formula = C 6H2BrCl3
E. None of the above are the proper empirical formula for bromotrichlorobenzene.
17. A substance has a molar mass of 131.39 g/mol with an empirical formula of C2HCl3. What is the molecular formula of this
substance?
A. CHCl
B. C2HCl3
C. C4H2Cl6
D. C6H3Cl12
E. Not enough information to calculate the proper molecular formula.
18. A 224 gram sample of a hydrocarbon was found to contain 32.0 grams of hydrogen. What is the EMPIRICAL formula of this
hydrocarbon (CXHY)?
A. C32H16
B. C24H4
C. C12H2
D. C6H
E. CH2
19. If the reaction below was balanced properly, what would be the stoichiometric coefficient in front of the O 2?
2 C10H20O +
A.
B.
C.
D.
E.
? O2 → 20 CO2 + 20 H2O
60
40
29
20
10
20. Circle any of the compounds below that would be SOLUBLE in water.
A. NaNO3
B. (NH4)2SO4
C. Li2CO3
D. (NH4)3PO4
E. None of the above would be soluble in water.
21. If aqueous lithium hydroxide was mixed with aqueous ammonium carbonate, what is one possible product from this
double replacement reaction?
A. LiNH4
B. OHCO3
C. Li2CO3
D. All of the above could form as products from this mixing.
E. None of the above would be possible products from this mixing.
22. If the reaction below was balanced properly, what would be the stoichiometric coefficient in front of the NH 4NO3?
3 Fe(NO3)2 + 2 (NH4)3PO4 → Fe3(PO4)2 + ?
A.
B.
C.
D.
E.
NH4NO3
1
2
3
4
6
23. RDX has the formula C3H6N6O6 and was developed as an explosive more powerful than TNT. If the decomposition reaction
below was balanced properly, what would be the stoichiometric coefficient in front of the oxygen gas?
2 C3H6N3(NO2)3 → 6 C + 6 N2 + 6 H2O +
A.
B.
C.
D.
E.
? O2
2
3
4
5
6
24. Select ALL statements below that are NOT correct. MARK ALL THAT APPLY.
A. The limiting reagent determines the maximum amount of product that can form.
B. The theoretical yield is the maximum amount of product that can form.
C. The reagent in EXCESS is consumed first in the reaction.
D. The percent yield is a measure of the efficiency of a reaction.
E. The actual yield is always greater than the theoretical yield.
25. If 90 moles of magnesium oxide decomposed according to the equation below, what is the theoretical yield of oxygen gas
(O2 in moles)?
2 MgO → 2 Mg + O2
A. 270 moles
B. 180 moles
C. 90 moles
D. 45 moles
E. None of the above.
26. Considering the reaction below, how many moles of nitrogen gas (N2) would be need to react with 30 moles of sodium
metal (Na)?
2 Na + 3 N2 → 2 NaN3
A. 60 moles
B. 45 moles
C. 30 moles
D. 15 moles
E. 10 moles
27. Considering the reaction below, how many moles of NH3 could be produced from a mixture of 12 moles of H2 and 30 moles
of N2? Hint: calculate the theoretical yield of NH3 based on the limiting reagent.
N2 + 3 H2 → 2 NH3
A.
B.
C.
D.
E.
60 moles
30 moles
24 moles
20 moles
8 moles
28. The water-gas shift reaction shown below is an industrial process used to generate hydrogen gas. If 150 moles of carbon
monoxide reacts with 250 moles of water, how much of the reagent in excess would be left unreacted when the limiting
reagent is fully consumed?
CO + H2O → CO2 + H2
A.
B.
C.
D.
E.
250 moles of H2O in excess left unreacted
100 moles of H2O in excess left unreacted
150 moles of CO in excess left unreacted
100 moles of CO in excess left unreacted
Neither CO or H2O is in excess
29. Syngas is produced from methane and water according to the reaction below. How many grams of water would be needed
to fully react with 10.0 grams of methane (CH4)?
CH4 + H2O → CO + 3 H2
A. 20.0 g
B. 11.3 g
C. 10.0 g
D. 8.89 g
E. Cannot determine from information provided.
30. A reaction has a theoretical yield of 200 grams with a percent yield of 60%. What is the actual yield for this reaction?
A. 333 g
B. 200 g
C. 120 g
D. 60 g
E. Cannot determine from information provided. The reaction would have to be provided.
FREE RESPONSE:
1.
(2 points) Draw a 4d orbital.
2.
(2 points) Write the balanced equation for the complete combustion of diesel fuel, C16H34.
3.
(2 points) Write the balanced equation for the reaction that occurs when aqueous calcium chloride is mixed with aqueous
ammonium carbonate. Be sure to write the phases of all components in the reaction.
4.
(2 points) If 10 grams of hydrogen gas is mixed with 90 grams of oxygen gas, predict the theoretical yield of water that
could be produce according to the reaction below.
2H2 + O2 → 2H2O
5.
(2 points) How many grams of magnesium metal (Mg) would be required to produce 12 grams of Carbon (C) from the
reaction below?
2 Mg + CO2 → 2 MgO + C
EXTRA CREDIT: (10 points) Show your work for credit; no partial credit will be awarded.
The mass of air relative to fuel used in an internal combustion engine is called the air-fuel ratio (AFR). It indicates the number of
grams of air that must be mixed with one gram of fuel in an engine for complete combustion. If the air provides the exact amount of
oxygen needed to completely combust all of the fuel, this ratio is known as the proper stoichiometric mixture. AFR is an important
measure for anti-pollution and performance-tuning reasons.
If air is approximately 23.3% oxygen by MASS, and the fuel used is C8H18 (gasoline), determine the stoichiometric air to fuel ratio
(grams of air required to combust one gram of fuel).
REFERENCE EQUATIONS:
Percent Yield (%) = [Actual Yield (g)/Theoretical Yield (g) ] x 100
Density = Mass / Volume
Number of Nodes in an electron orbital = n-1 where n = principal quantum number