CHEMISTRY 102A
Hour Exam II
1.
My answers for this Chemistry 102 exam should be graded with the answer sheet
associated with:
a) Form A
2.
b) Form B
c) Form C
d) Form D
e) Form E
A sample of LSD (D-lysergic acid diethylamide, C24H30N3O, molar mass = 376.51
g/mol) is added to sodium chloride (NaCl) to form a mixture. Given that a 1.00 gram
sample of the mixture undergoes complete combustion to produce 1.20 grams of CO2,
what is the mass percentage of LSD in the mixture? The molar mass of CO2 is 44.01
g/mol. Assume the only carbon containing product is CO2.
a) 10.%
3.
Spring 2012
b) 12%
c) 38%
d) 43%
e) 59%
If 2.00 L of 1.00 M K2S is mixed with 1.00 L of 1.00 M KHSO4, what is the
concentration of potassium ions in the final solution?
a) 0.667 M
b) 1.00 M
c) 1.33 M
d) 1.67 M
e) 2.00 M
______________________________________
4.
A compound contains only carbon, hydrogen, and oxygen. Combustion of 0.635 g of
the compound produces 1.602 g CO2 and 0.2810 g H2O. What is the mass percent of
hydrogen in the unknown compound?
a) 6.98% H
5.
b) 4.95% H
c) 2.48% H
d) C3H8O
e) C3H3O
A student added 50.0 mL of an NaOH solution to 100.0 mL of 0.400 M HCl. The
solution was then treated with an excess of aqueous Cr(NO3)3, resulting in formation of
2.06 g of precipitate. Calculate the concentration of the initial NaOH solution. The
molar mass of the precipitate is 103.02 g/mol.
a) 2.0 M
7.
e) 88.5% H
A compound contains only carbon, hydrogen, and oxygen. Combustion of 0.635 g of
the compound produces 1.602 g CO2 and 0.2810 g H2O. What is the empirical formula
of the compound?
a) C7H6O2
b) C2H2O
c) C3H2O3
________________________________________
6.
d) 44.3% H
b) 1.0 M
c) 2.4 M
d) 1.2 M
e) 0.50 M
Which of the following substances should have the largest value of b in the van der
Waals equation?
a) He
b) O2
c) CO2
d) H2O
e) Ne
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CHEMISTRY 102A
Hour Exam II
Spring 2012
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8.
When 2.00 L of 2.00 M Cu(NO3)2 is added to 1.50 L of 2.00 M K3PO4, a precipitate
forms. Which of the following (a-d) is the correct net ionic equation for this precipitation
reaction?
a) Cu4+(aq) + PO43(aq)  Cu3(PO4)4(s)
b) Cu2+(aq) + PO46(aq)  Cu3PO4(s)
c) Cu2+(aq) + PO43(aq)  CuPO4(s)
d) Cu4+(aq) + PO46(aq)  Cu6(PO4)4(s)
e) None of the above (a-d) are the correct net ionic equation.
9.
When 2.00 L of 2.00 M Cu(NO3)2 is added to 1.50 L of 2.00 M K3PO4, a precipitate
forms. How many moles of precipitate can form?
a) 1.00 mol
b) 1.33 mol
c) 1.50 mol
d) 1.75 mol
e) 2.00 mol
___________________________________________________
10.
Consider three identical flasks filled with different gases at the following conditions:
Flask A: CO(g) at 760. torr and 0C
Flask B: N2(g) at 250. torr and 0C
Flask C: H2(g) at 100. torr and 0C
Which flask contains the gas sample having the greatest average kinetic energy (per
molecule) and which flask contains the gas sample having the greatest average velocity
(per molecule)?
a) The gas in flask A has the greatest average kinetic energy and the gas in flask B has
the greatest average velocity.
b) All gases in the various flasks have the same average kinetic energy and the gas in
flask C has the greatest average velocity.
c) The gas in flask C has the greatest average kinetic energy and all gases in the various
flasks have the same average velocity.
d) All gases in the various flasks have the same average kinetic energy and the gas in
flask B has the greatest average velocity.
e) All gases in the various flasks have the same average kinetic energy and the same
average velocity.
11.
A certain compound contains 49.02% carbon, 2.74% hydrogen and the rest chlorine by
mass. What is the empirical formula of the compound?
a) C3H2Cl
b) C3H3Cl2
d) CHCl2
e) C4H3Cl
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c) C2HCl2
CHEMISTRY 102A
Hour Exam II
12.
A gas sample containing 1.50 moles at 25°C exerts a pressure of 400. torr. Some gas is
added to the same container and the temperature is also increased to 50.°C. If the
pressure increases to 800. torr, how many moles of gas were added to the container?
Assume a constant volume container.
a) 3.25 mol
13.
Spring 2012
b) 6.00 mol
c) 1.50 mol
d) 1.75 mol
e) 1.27 mol
Dinitrogen tetrafluoride, N2F4, and HF can be produced by the reaction of NH3 with F2 as
illustrated in the following unbalanced equation:
NH3(g) + F2(g)  N2F4(g) + HF(g)
If 4.00 g of NH3 and 14.0 g of F2 are allowed to react, what mass of HF can be
produced? Molar mass NH3 = 17.03 g/mol; molar mass F2 = 38.00 g/mol; molar mass
HF = 20.01 g/mol.
14.
a) 5.23 g HF
b) 7.77 g HF
d) 14.1 g HF
e) 18.0 g HF
c) 8.85 g HF
Some very effective rocket fuels are composed of lightweight liquids. The fuel
composed of dimethylhydrazine [(CH3)2N2H2] mixed with dinitrogen tetroxide was used
to power the Lunar Lander in its missions to the moon. The two components react
according to the following equation:
(CH3)2N2H2(l) + 2 N2O4(l)  3 N2(g) + 4 H2O(g) + 2 CO2(g)
If 150 g of dimethylhydrazine reacts with excess dinitrogen tetroxide and the product
gases are collected at 27°C in an evacuated 250 L tank, what is the partial pressure of
nitrogen gas produced and what is the total pressure in the tank assuming the reaction has
100% yield? The molar mass of dimethylhydrazine is 60.1 g/mol.
15.
a) 0.25 atm; 1.0 atm
b) 0.25 atm; 1.3 atm
d) 0.50 atm; 1.9 atm
e) 0.74 atm; 2.2 atm
c) 0.50 atm; 1.5 atm
Consider the following generic equation (which is assumed balanced):
3A + B  2C + D
2.0 mol A and 1.0 mol B react to form 1.0 mol C. What is the percent yield of this
reaction?
a) 12.5%
b) 25%
c) 50.%
d) 75%
e) 100%
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CHEMISTRY 102A
Hour Exam II
16.
Spring 2012
A 6.50 g sample of a diprotic acid (abbreviated H2A in the balanced equation below)
requires 137.5 mL of a 0.750 M NaOH solution for complete reaction. Calculate the
molar mass of the acid.
H2A(aq) + 2 NaOH(aq)  2 H2O(l) + Na2A(aq)
a) 15.9 g/mol
17.
c) 63.0 g/mol
d) 103 g/mol
e) 126 g/mol
Equal moles of N2 gas and O2 gas are mixed in a flexible reaction vessel and are then
ignited to form gaseous N2O. Assuming that the reaction goes to completion, what is the
ratio of the final volume of the gas mixture to the initial volume of the gas mixture
(Vfinal:Vinitial = ?) if both volumes are measured at the same temperature and pressure?
(Hint: Nitrogen gas is the limiting reactant and don’t forget to balance the equation.)
a) 3:4
18.
b) 31.5 g/mol
b) 2:3
c) 3:2
d) 2:1
e) 1:2
Which of the following gases has the largest density at STP?
a) He
b) Ne
c) Ar
d) Kr
e) All of the gases have the same density at STP.
19.
Gas A has an effusion rate which is nine (9) times faster than that of gas B. Which of the
following statements is true concerning the molar masses of gases A and B?
a)
b)
c)
d)
e)
20.
Gas A has a molar mass that is 3 times heavier than gas B.
Gas A has a molar mass that is 9 times heavier than gas B.
Gas A has a molar mass that is 81 times heavier than gas B.
Gas B has a molar mass that is 3 times heavier than gas A.
Gas B has a molar mass that is 81 times heavier than gas A.
Which of the following statements is false?
a) Real gas molecules have a volume.
b) Real gas molecules exert attractive forces on one another.
c) Gases tend to behave most ideally when the container volume is small and when gas
molecules have a relatively slow average velocity.
d) As temperature increases, the average kinetic energy of a sample of gas molecules
increases.
e) At constant temperature, lighter gas molecules move at a faster average velocity than
heavier gas molecules.
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CHEMISTRY 102A
Hour Exam II
21.
22.
Spring 2012
Which of the following compounds has the highest vapor pressure at -100°C?
a) NH3
b) PH3
d) SbH3
e) H2O
c) AsH3
Which of the following statements (a-d) is true?
a) In general, covalent intermolecular forces are stronger than the intermolecular forces
in ionic compounds.
b) Substances with very weak intermolecular forces are solids at room temperature.
c) Intermolecular forces are much stronger than intramolecular forces (bonds).
d) As temperature increases, the vapor pressure of a liquid increases.
e) None of the above statements (a-d) are true.
23.
Phosphorus can be prepared from calcium phosphate by the following reaction:
2 Ca3(PO4)2(s) + 6 SiO2(s) + 10 C(s)  6 CaSiO3(s) + P4(s) + 10 CO(g)
Phosphorite is a mineral which contains Ca3(PO4)2 plus other non-phosphorus containing
compounds. What is the maximum amount of P4 that can be produced from 1.0 kg of
phosphorite if the phorphorite sample is 75% Ca3(PO4)2 by mass? Assume an excess of
the other reactants. Molar mass Ca3(PO4)2 = 310.18 g/mol; molar mass P4 = 123.88
g/mol.
24.
25.
a) 0.75 kg
b) 0.15 kg
d) 0.38 kg
e) 0.20 kg
c) 0.50 kg
When Mg(s) reacts with HBr(aq), MgBr2(aq) and H2(g) are produced. What mass of
magnesium is required to react completely with 20.2 g of HBr?
a) 3.0 g
b) 12 g
d) 10. g
e) 0.13 g
c) 6.1 g
The boiling points of the halogens increase when going from F2 to I2. What type of
intermolecular forces are responsible for this trend?
a)
b)
c)
d)
dipole-dipole forces
hydrogen bonding forces
London dispersion forces
electrostatic (ionic) forces
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CHEMISTRY 102A
Hour Exam II
26.
Spring 2012
How many of the following five compounds are strong electrolytes?
I.
II.
III.
IV.
V.
cobalt(II) nitrate
ammonium chromate
hydrofluoric acid
strontium hydroxide
magnesium sulfate
a) 1
b) 2
c) 3
d) 4
e) 5 (All five of the above compounds are strong electrolytes.)
27.
A sealed weather balloon containing 0.200 mol of He(g) rises to 15 km above the earth’s
surface. At this altitude, the volume of the balloon is 37.0 L at a pressure of 76.0 torr.
What is the temperature of the earth’s atmosphere at 15 km above the surface?
a) −225°C
28.
b) −87°C
c) −48°C
d) −5°C
e) 22°C
Consider the products for the following four aqueous reactions:
I. FeSO4(aq) + NaCl(aq) 
II. Pb(NO3)2(aq) + MgCl2(aq) 
III. CaCl2(aq) + (NH4)2SO4(aq) 
IV. K2S(aq) + Ni(NO3)2(aq) 
Which reactions result in the formation of a precipitate?
29.
30.
a) II and III
b) I, II and III
d) I and III
e) II and IV
c) II, III and IV
How many of the following four statements is/are true?
I.
II.
III.
IV.
A concentrated solution in water will always contain a strong or weak electrolyte.
A strong electrolyte will break up into ions when dissolved in water.
All covalent compounds are nonelectrolytes in water.
All ionic compounds are strong electrolytes in water.
a)
0 (All are false.)
b) 1
c) 2
d) 3
e) 4 (All are true.)
Consider the following pairs of compounds. Which compound in each pair has the
higher boiling point? In CH2O, carbon is the central atom.
N2 vs CO
H3C-CH3 vs CH2O
HF vs KNO3
a) CO; CH2O; KNO3
b) N2; CH2O; KNO3
d) CO; H3CCH3; HF
e) N2; H3CCH3; KNO3
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c) N2; CH2O; HF
CHEMISTRY 102A
Hour Exam II
Spring 2012
USEFUL CONSTANTS/EQUATIONS
K = °C + 273
M = Molarity =
mol solute
L solution
PV = nRT
% yield =
1 kg = 1000 g
R = 0.08206 L atm/K mol
1 L = 1000 mL
1 atm = 760 torr = 760 mm Hg
rate1

rate 2
M2
M1
Ptotal = P1 + P2 + P3 + ...
STP = 1 atm, 273 K
Avogadro's number, N = 6.022 × 1023
Mass % of A =
actual
(100)
theoretical
mass of A(100)
totalmass
(M  molar mass)
KEAVE = (3/2) RT, R = 8.3145 J/Kmol
d = density = mass/volume
PM = dRT, M = molar mass
P1V1
PV
 2 2
n1T1
n 2 T2
Kinetic Energy = (1/2) mv2

an 2 
P

(V
 nb)  nRT
 measured
V 2  measured

Solubility rules:
1. Most nitrate salts are soluble.
2. Most salts of alkali metals and ammonium cations are soluble.
3. Most chloride, bromide, and iodide salts are soluble.
Exceptions: salts containing Ag+, Pb2+, and Hg22+ ions are insoluble.
4. Most sulfate salts are soluble.
Exceptions: sulfates containing Ca2+, Ba2+, Pb2+, and Hg22+ ions are insoluble.
5. Most hydroxide salts are insoluble.
Exceptions: hydroxides containing alkali metals, Ba2+, Sr2+, and Ca2+ ions are soluble.
6. Most sulfide, carbonate, chromate, and phosphate salts are insoluble.
Exceptions: salts of alkali metals and ammonium cations are soluble.
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