GENERAL CHEMISTRY I
CHEM 1311.002 (12681)
EXAM 3
Monday, June 25, 2012
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Part 1: Empirical Formulas
1.
A compound known to contain only the elements carbon and hydrogen was analyzed and found to contain 85.63% carbon by
mass. What is the empirical formula of this compound? Atomic weights: C 12.01
H 1.008
a) CH
2.
d) CH4
e) CH5
b) NCl2
c) NCl3
d) N2Cl3
e) N2Cl5
A compound known to contain only the elements chromium and sulfur was analyzed and found to contain 51.95% chromium
by mass. What is the empirical formula of this compound? Atomic weights: Cr 52.00
S 32.07
a) CrS
4.
c) CH3
A 5.000 g sample of a compound known to contain only the elements nitrogen and chlorine was analyzed and found to
contain 0.582 g of nitrogen. What is the empirical formula of this compound? Atomic weights: N 14.01
Cl 35.45
a) NCl
3.
b) CH2
b) CrS2
c) CrS3
d) Cr2S3
e) Cr2S5
A 5.000 g sample of a compound known to contain only the elements phosphorus and oxygen was analyzed and found to
contain 2.182 g of phosphorus. What is the empirical formula of this compound? Atomic weights: P 30.97
O 16.00
a) PO
b) P2O
c) PO2
d) P2O3
e) P2O5
Part 2: Molecular Formulas
5.
A compound known to contain only the elements carbon and hydrogen was analyzed and found to contain 92.26% carbon by
mass and have a molecular weight of 52.07 g/mol. How many hydrogen atoms are present in each molecule of this
compound? Atomic weights: C 12.01
H 1.008
a) 1
6.
d) 4
e) 5
b) 2
c) 3
d) 4
e) 5
A compound known to contain only the elements sulfur and oxygen was analyzed and found to contain 59.95% oxygen by
mass and have a molecular weight of 80.07 g/mol. How many sulfur atoms are present in each molecule of this compound?
Atomic weights: S 32.07
O 16.00
a) 1
8.
c) 3
A 5.000 g sample of a compound known to contain only the elements nitrogen and oxygen was analyzed and found to contain
1.297 g of nitrogen and have a molecular weight of 108.0 g/mol. How many oxygen atoms are present in each molecule of
this compound? Atomic weights: N 14.01
O 16.00
a) 1
7.
b) 2
b) 2
c) 3
d) 4
e) 5
A 5.000 g sample of a compound known to contain only the elements carbon and fluorine was analyzed and found to contain
4.318 g of fluorine and have a molecular weight of 88.01 g/mol. How many fluorine atoms are present in each molecule of
this compound? Atomic weights: C 12.01
F 19.00
a) 1
b) 2
c) 3
d) 4
e) 5
Part 3: Basic Reaction Stoichiometry (identity of limiting reactant known from beginning of problem)
9.
The combustion of methane (CH4) is described by the following equation:
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
If 13.48 g of CH4 reacts in the presence of excess O2 what mass of CO2 will be formed? Assume complete reaction.
Atomic weights: C 12.01
H 1.008
O 16.00
a) 11.55 g
10
c) 36.98 g
d) 59.81 g
e) 72.14 g
.How many grams of H2O are produced in the reaction shown in question 9?
a) 7.217 g
11.
b) 19.41 g
b) 12.84 g
c) 19.56 g
d) 30.28 g
e) 45.61 g
How many grams of O2 are consumed in the reaction shown in question 9? Assume complete reaction.
a) 12.91 g
b) 26.14 g
c) 53.78 g
d) 77.41 g
e) 94.16 g
Part 4: Advanced Reaction Stoichiometry (includes limiting reactant and percent yield concepts)
12.
Hydrogen and fluorine combine to form hydrogen fluoride, as described by the following equation:
H2(g) + F2(g)  2HF(g)
If a sealed reaction vessel contains 15.00 g of H2 and 25.00 g of F2 gases, what is the maximum possible mass (theoretical
yield) of HF that can be formed? Atomic weights: H 1.008
F 19.00
a) 12.83 g
13.
d) 32.03
e) 39.51
b) F2
For the reactant that you found to be the excess reactant in question 12, how many grams of it remain at the end of the
reaction? Assume 100% yield.
a) 0.49 g
15.
c) 26.33 g
Which reactant did you find to be the limiting reactant in question 12?
a) H2
14.
b) 17.48 g
b) 7.97 g
c) 13.67 g
d) 22.52 g
e) 27.17 g
If the reaction in question 12 produces 10.83 g of HF, what is the percent yield?
a) 27.41%
b) 33.75%
c) 41.13%
d) 61.96%
e) 84.41%
Part 5: Solution Concentration and Solution Stoichiometry
16.
If 30.06 g of NaCl is dissolved in enough water to produce 250.0 mL of solution, what is the molarity of the solution?
Atomic weights: Na 22.99
Cl 35.45
a) 1.308 M
17.
d) 5.227 M
b) 21.27 mL
c) 29.73 mL
d) 46.10 mL
If a solution of MgBr2 has a concentration of 1.413 M, what mass of MgBr 2
Atomic weights: Mg 24.31
Br 79.90
a) 3.197 g
19.
c) 3.968 M
e) 6.823 M
If a CaCl2 solution has a concentration of 2.850 M, how many milliliters of the solution must you take in order to get 14.58 g
of CaCl2? Atomic weights: Ca 40.08
Cl 35.45
a) 13.47 mL
18.
b) 2.057 M
b) 6.504 g
c) 8.312 g
e) 65.11 mL
is contained in 25.00 mL of the solution?
d) 12.44 g
e) 17.83 g
When solutions of hydrochloric acid (HCl) and sodium hydroxide (NaOH) are mixed, a neutralization reaction occurs, as
described by the following equation:
HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)
What volume of 1.552 M HCl solution is required to neutralize 25.00 mL of 2.206 M NaOH solution?
a) 16.43 mL
20.
b) 24.18 mL
c) 35.53 mL
d) 48.27 mL
e) 62.13 mL
When solutions of nitric acid (HNO3) and potassium hydroxide (KOH) are mixed, a neutralization occurs, as described by the
following equation:
HNO3(aq) + KOH(aq)  HOH(l) + KNO3(aq)
If a 25.00 mL sample of a KOH solution requires 16.43 mL of 1.683 M HNO 3 to neutralize it, what is the concentration of
the KOH solution?
a) 0.743 M
b) 1.106 M
c) 1.893 M
d) 2.213 M
e) 2.997 M
Part 6: Solubility, Precipitates, and Spectator Ions
21.
When aqueous solutions of barium nitrate and ammonium chloride are mixed, which ions are spectator ion?
a) Ba2+, Cl-
22.
b) NH4+, NO3-
c) Ba2+, NH4+, Cl-, NO3-
Did a precipitate form in the mixing described in question 21?
a) Yes, a precipitate of barium chloride formed.
b)Yes, a precipitate of ammonium nitrate formed.
c) Yes, both barium chloride and ammonium nitrate formed as precipitates.
23.
d) There are no spectator ions
d) No, there was no precipitate.
When aqueous solutions of calcium bromide and sodium sulfate are mixed, which ions are spectator ions?
a) Ca2+, SO42-
b) Na+, Br-
c) Ca2+, Na+, SO42-, Br-
d) There are no spectator ions
24.
Did a precipitate form in the mixing described in question 23?
a) Yes, a precipitate of calcium sulfate formed.
b) Yes, a precipitate of sodium bromide formed.
c) Yes, both calcium sulfate and sodium bromide formed as precipitates.
25.
d) No, there was no precipitate.
Is there a net ionic equation for the mixing described in question 23?
a) Yes. The equation is:
Ca2+(aq) + SO42-(aq)  CaSO4(s)
b) Yes. The equation is:
Na+(aq) + Br-(aq)  NaBr(s)
c) Yes. The equation is:
Ca2+(aq) + 2Na+(aq) + SO42-(aq) + 2Br-(aq)  CaSO4(s) + 2NaBr(s)
d) No. There is no net ionic equation.
*** END OF EXAM 3 ***
The remaining pages provide supplemental data to help you in solving the problems on this exam.