VERSION B
Chem 142
Summer 2011
CHEM 142 - Exam 2
Version B
!!! DO NOT OPEN THIS EXAM BOOK UNTIL
TOLD TO DO SO BY THE INSTRUCTOR !!!
Instructor: Dr. Kari Pederson NO GRAPHING CALCULATORS ALLOWED
Date:
Friday, August 5
Time:
9:40-10:40am
ONLY CALCULATORS MAY BE USED AS CALCULATORS
(you may not use your cellular phone as a calculator)
NO HEADPHONES ALLOWED (EARPLUGS ARE OK)
Location: BAG 154
NO HATS WITH BRIMS ALLOWED
!!! PLEASE READ THIS !!!
Indicate all of the following on your scantron form or five points
will be deducted from your exam score:
First Name, Last Name, Student Number, Section, Exam Version
YOUR FULL NAME:
_______________________
first name
________________________
last name
YOUR SECTION/SEAT:
________________________
discussion section
________________________
seat number
VERSION B
Page 1 of 11
EXAM 1
VERSION B
Chem 142
Question
Points Possible
1-8
24
9-16
40
17-24
16
25
20
Scantron Info?
-5
TOTAL
EXAM 1
Summer 2011
Score
100
VERSION B
Page 2 of 11
Chem 142
VERSION B
Summer 2011
MULTIPLE CHOICE: CONCEPTS. 8 @ 3 pts each  24 POINTS TOTAL
Please mark the one correct answer for each of the following questions on your scantron.
1.
Which of the following statements is(are) true?
Oxidation and reduction
I.
cannot occur independently of each other.
II.
result in a change in the oxidation states of the species involved.
III.
describe the loss and gain of electron(s), respectively.
IV.
accompany all chemical changes.
A)
B)
C)
D)
E)
2.
I only
II only
III only
IV only
I, II, and III
In which of the following compounds does sulfur have the most positive oxidation
state?
A) SO
S: +2
B) SF6
S: +6
C) MgSO3
S: +4
D) H2S
S: -2
E) SO2
S: +4
3.
A rigid container contains 10.0 g of neon gas. With the temperature kept constant,
10.0 g of argon gas is added. What happens?
A) The pressure in the container doubles.
B) The pressure in the container increases by less than a factor of 2.
C) The pressure in the container increases by more than a factor of 2.
D) The pressure stays the same size, but the volume increases.
E) The pressure decreases by a factor of 2.
P ! n  10.0g Ar fewer moles than 10.0g Ne means total number of moles will increase
by less than a factor of two, therefore total pressure will increase by less than a factor of
two.
EXAM 1
VERSION B
Page 3 of 11
Chem 142
VERSION B
Summer 2011
4.
Which of the following statements is true concerning ideal gases?
A) The gas particles in a sample exert attraction on one another.
B) The temperature of the gas sample is linearly related to the average velocity of
the gas particles.
C) At STP, 1.0 L of Ar (g) contains about twice the number of atoms as 1.0 L of
Ne (g) because the molar mass of Ar is about twice that of Ne.
D) A gas exerts pressure as a result of the collisions of the gas molecules with the
walls of the container.
E) All of these statements are false.
5.
Consider separate samples of Ar (g) and Ne (g). For what ratio of absolute
temperatures (Ne:Ar) are the average kinetic energies equal?
A) 1.98:1
B)
2 :1
C) 1:1
D) 1: 2
E) none of these
6.
Four identical 1.0 L flasks contain the gases Ne, CH4, N2, and F2, each at 0°C and 1
atm pressure. For which gas do the molecules have the highest root mean square
velocity (urms)?
A) Ne
B) CH4
C) N2
D) F2
E) The molecules of all the gases have the same root mean square velocity.
1
 Lowest MM corresponds to highest urms
!
MM
urms
7.
Consider the reaction CH4 (g) + CO2 (g) ! 2C (s) + 2H2O (g). A 6.5 L vessel was
initially filled with pure CO2, at a pressure of 5.2 atm, at 300 K. After equilibrium was
reached, the volume was decreased to 4.0 L, while the temperature was kept at 300
K. This will result in ___________.
A) an increase in Kp.
B) a decrease in Kp.
C) a shift in the equilibrium position to the right (products).
D) a shift in the equilibrium position to the left (reactants).
E) none of these
EXAM 1
VERSION B
Page 4 of 11
Chem 142
8.
VERSION B
Summer 2011
The K for the reaction, NH3 (aq) + H2O (l) ! OH- (aq) + NH4+ (aq), is called
A) Kb for NH4+
B) Kb for NH3
C) Ka for NH4+
D) Ka for NH3
E) none of the above
EXAM 1
VERSION B
Page 5 of 11
Chem 142
VERSION B
Summer 2011
MULTIPLE CHOICE: SHORT CALCULATIONS. 8 @ 5 pts each  40 TOTAL POINTS
Please mark the one correct answer for each of the following questions on your scantron.
9.
A student weighs out 0.768 g of KHP (molar mass = 204 g/mol) and titrates to the
equivalence point with 32.72 mL of a stock NaOH solution. What is the
concentration of the stock NaOH solution? KHP is an acid with one acidic proton.
A) 0.100 M
B) 3.15 M
C) 0.115 M
D) 0.0757 M
E) none of these
1mol KHP
0.768g KHP !
= 3.76 ! 10 "3 mol KHP
204g KHP
1mol NaOH
3.76 ! 10 "3 mol KHP !
= 3.76 ! 10 "3 mol NaOH
1mol KHP
"3
3.76 ! 10 mol NaOH
= 0.115M NaOH
0.03272L
10. A balloon is inflated with helium to a volume of 3.8 L at 32°C. If you take the
balloon outside on a cold day (17°C), what will be the new volume of the balloon?
A) 3.6 L
B) 4.0 L
C) 1.9 L
D) 7.6 L
E) none of the above
V1 V2
V
3.8L
=
! V2 = 1 " T2 =
" 290K = 3.6L
T1 T2
T1
305K
EXAM 1
VERSION B
Page 6 of 11
Chem 142
VERSION B
Summer 2011
11. A piece of magnesium metal undergoes complete reaction with hydrochloric acid as
follows:
Mg (s) + 2 HCl (aq)  MgCl2 (aq) + H2 (g)
The hydrogen gas generated is collected over water at 25°C. The volume of gas is
734 mL measured at 1.00 atm. How many grams of magnesium reacted? (The vapor
pressure of water at 25°C is 0.0313 atm.)
A) 7.30 g
B) 0.729 g
C) 0.707 g
D) 8.43 g
E) none of the above
PH 2 = Ptotal ! PH 2 O = 1.00atm ! 0.0313atm = 0.9687atm
PV
0.9687atm " 0.734L
PV = nRT ! n =
=
= 2.91 # 10 $2 mol H 2
RT 0.08206 L " atm " 298K
mol " K
1mol
Mg
2.91 ! 10 "2 mol H 2 !
= 2.91 ! 10 "2 mol Mg
1mol H 2
24.3050g Na
2.91 ! 10 "2 mol Na !
= 0.707g Mg
1mol Na
12. The diffusion rate of H2 gas is 6.47 times as great as that of a certain noble gas (both
gases are at the same temperature). What is the noble gas?
A) He
B) Ne
C) Ar
D) Kr
E) Xe
rate1
=
rate2
2
# rate1
&
! MM 2 = %
" MM 1 ( = 6.47 " 2
$ rate2
'
MM 1
MM 2
(
)
2
= 83.8 g mol ! Kr
13. A flask with a volume of 0.125 L contains 0.1016 grams of an unknown gas at 20.0°C
and 0.968 atm. What is the molar mass of the gas?
A) 16.0 g/mol
B) 20.2 g/mol
C) 32.0 g/mol
D) 40.0 g/mol
E) none of the above
L # atm '
$
0.08206
&
) 293K
m
m RT 0.1016g %
mol # K (
PV =
RT ! MM = "
=
= 20.2 g mol
MM
V
P
0.125L
0.968atm
EXAM 1
VERSION B
Page 7 of 11
Chem 142
VERSION B
Summer 2011
14. The equilibrium constant for Br2 (g) + Cl2 (g) ! 2BrCl (g) at 25°C is 48. What is the
equilibrium constant for 4BrCl (g) ! 2Br2 (g) + 2Cl2 (g) at the same temperature?
A) -48
B) 4.3 x 10-4
C) 0.021
D) 96
E) -2300
"2
K ! = K "2 = ( 48 ) = 4.3 # 10 "4
15. For the reaction 2NO (g) + Br2 (g) ! 2NOBr (g), Kc = 0.50 at 100°C. An equilibrium
mixture is found to contain [NO]=[NOBr]=0.20 M. What is the concentration of Br2
(g) in the flask?
A) 1.00 M
B) 0.50 M
C) 2.00 M
D) 2.50 M
E) none of the above
2
2
NOBr ]
NOBr ]
[
[
Kc =
! [ Br2 ] =
[ NO ]2 [ Br2 ]
[ NO ]2 K c
=
0.2 2
= 2.00M
0.2 2 " 0.5
16. A sample of NaOH is found to have a pH of 9.60. This solution is _______.
A) acidic with [NaOH]=4.0 x 10–5 M and pOH=9.60
B) acidic with [NaOH]=2.5 x 10–4 M and pOH=4.40
C) basic with [NaOH]=4.0 x 10–5 M and pOH=4.40
D) basic with [NaOH]=2.5 x 10–4 M and pOH=4.40
E) basic with [NaOH]=2.5 x 10–4 M and pOH=9.60
pH > 7  basic
pOH = 14.00 ! 9.60 = 4.40
"#OH ! $% = 10 !4.40 = 4.0 & 10 !5 M OH !
1mol NaOH
4.0 ! 10 "5 M OH " !
= 4.0 ! 10 "5 M NaOH
1mol OH "
EXAM 1
VERSION B
Page 8 of 11
Chem 142
VERSION B
Summer 2011
MATCHING. 8 @ 2 pts each  16 POINTS TOTAL
Please indicate the letter of the one best answer for each of the following questions in the
blank. Each answer is used no more than once.
17. Chemical equilibrium is macroscopically_____E_______.
18. The following reaction represents a _____G_________ equilibria.
H2 (g) + F2 (g) ! 2HF (g)
19. The following is an example of a ________T___________ reaction.
Mg (s) + 2 HCl (aq) ! MgCl2 (aq) + H2 (g)
20. In a ________Lor U_____________ reaction, water is usually formed as one of the
products.
21. For the following reaction, Kc is _____H______ Kp.
Br2 (l) + H2 (g) ! 2 HBr (g)
22. For a certain reaction at 25.0°C, the value of K is 3.4 × 10-1. At 50.0°C the value of K
is 1.2 × 10-3. This means that the reaction is _____F______.
23. HClO is best classified as a _____N_________.
24. HPO42- is the ______R_______ of H2PO4-.
A)
E)
I)
M)
Q)
T)
dynamic
static
equal to
strong acid
conjugate acid
single replacement
EXAM 1
B) endothermic
F) exothermic
J) combination
N) weak acid
R) conjugate base
U) combustion
C)
G)
K)
O)
S)
heterogeneous D)
homogeneous H)
decompostion L)
strong base
P)
double replacement
VERSION B
greater than
less than
neutralization
weak base
Page 9 of 11
VERSION B
Chem 142
Summer 2011
LONG ANSWER. 20 POINTS TOTAL
25. The following reaction occurs in acidic solution:
IO4- (aq) + Cu+ (aq) ! IO3- (aq) + Cu2+ (aq)
A) What is the balanced equation for this reaction? (6 pts)
oxidation: Cu+ (aq) ! Cu2+ (aq)
reduction: IO4- (aq) ! IO3- (aq)
balance everything but O and H
oxidation: Cu+ (aq) ! Cu2+ (aq)
reduction: IO4- (aq) ! IO3- (aq)
balance O with H2O
oxidation: Cu+ (aq) ! Cu2+ (aq)
reduction: IO4- (aq) ! IO3- (aq) + H2O (l)
balance H with H+
oxidation: Cu+ (aq) ! Cu2+ (aq)
reduction: IO4- (aq) + 2H+ (aq) ! IO3- (aq) + H2O (l)
balance charges with eoxidation: Cu+ (aq) ! Cu2+ (aq) + ereduction: IO4- (aq) + 2H+ (aq) + 2e- ! IO3- (aq) + H2O (l)
Equalize electron transfer
oxidation: 2 (Cu+ (aq) ! Cu2+ (aq) + e-)
reduction: IO4- (aq) + 2H+ (aq) + 2e- ! IO3- (aq) + H2O (l)
Balanced:
2Cu+ (aq) + IO4- (aq) + 2H+ (aq) ! 2Cu2+ (aq) + IO3- (aq) + H2O (l)
Please use your answer from part A for the calculations in parts B-C. If you are
unable to write a balanced equation, use the following balanced chemical reaction
for the remainder of the problem:
MnO2 (s) + 2Ag+ (aq) + 4H+ (aq)  Mn2+ (aq) + 2Ag2+ (aq) + 2H2O (l)
B) What is the equilibrium constant expression, Kc, for your balanced reaction?
(2 pts)
2
!"Cu 2 + #$ !" IO3% #$
Kc =
2
2
!"Cu + #$ !" IO4% #$ !" H + #$
EXAM 1
2
OR
!" Ag 2 + #$ !" Mn 2 + #$
Kc =
2
4
!" Ag + #$ !" H + #$
VERSION B
Page 10 of 11
VERSION B
Chem 142
Summer 2011
C) A laboratory chemist mixes 1.0 mol of each aqueous and gaseous product or
reactant in a rigid 2.0 L container. After the reaction reaches equilibrium, 1.25 mol of
the Cu2+ (or Ag2+) is observed.
i) When the system has reached equilibrium, what are the concentrations of all
aqueous and gaseous reactants and products? (10 pts)
[Cu+]
0.5
-2x
0.5-2x
Initial
Change
Equilibrium
[IO4-]
0.5
-x
0.5-x
[H+]
0.5
-2x
0.5-2x
[Cu2+]
0.5
+2x
0.5+2x
[IO3-]
0.5
+x
0.5+x
1.25mol
0.5 + 2x = 0.625 ! x = 0.0625M
= 0.625M
2.0L
!"Cu + #$ = 0.375M , "# IO4! $% = 0.4375M , !" H + #$ = 0.375M , !"Cu 2 + #$ = 0.625M ,
At equilibrium, !"Cu 2 + #$ =
"# IO3! $% = 0.5625M
OR
[Ag+]
0.5
-2x
0.5-2x
Initial
Change
Equilibrium
[H+]
0.5
-4x
0.5-4x
[Mn2+]
0.5
+x
0.5+x
[Ag2+]
0.5
+2x
0.5+2x
1.25mol
0.5 + 2x = 0.625 ! x = 0.0625M
= 0.625M
2.0L
!" Ag + #$ = 0.375M , !" H + #$ = 0.25M , !" Mn 2 + #$ = 0.5625M , !" Ag 2 + #$ = 0.625M
At equilibrium, !" Ag 2 + #$ =
ii) What is the value of Kc? (2 pts)
2
!"Cu 2 + #$ !" IO3% #$
0.625M ) ( 0.5625M )
(
%2
Kc =
=
2
2 = 25M
+ 2
%
+ 2
( 0.375M ) ( 0.4375M ) ( 0.375M )
!"Cu #$ !" IO4 #$ !" H #$
2
OR
! Ag 2 + #$ !" Mn 2 + #$ ( 0.625M )2 ( 0.5625M )
Kc = "
= 400
2
4 =
( 0.375M )2 ( 0.25M )4
!" Ag + #$ !" H + #$
2
EXAM 1
VERSION B
Page 11 of 11