Exam 2a

General Chemistry II - CHEM 112
EXAM II
Thursday, Oct. 16, 2014
Name (Printed): Solutions
Section:
Instructions: This test is closed book and closed notes. Calculators are also allowed, although
preprepared programs, integration and equation solving routines are not. Credit is dependent on
showing all steps in the calculation on this test. Clearly state any assumptions or approximations
you use to solve the problems. (6 problems, 105 pts)
R = 8.31441 J/K-mol
1 atm = 760 Torr
= 0.08206 L-atm/K-mol
0 C = 273.15 K
23
-1
NA = 6.02210 mol
−14
pKw = 14.0
Kw = 10
−3
3
3
10 L = 1 mL = 1 cm
1 mol = 10 mmol
6
9
10
1 m = 100 cm = 1000 mm = 10 m = 10 nm = 10 Å
0.001 kg = 1 g = 1000 mg
density of water:  = 1.00 g/ml = 1.00 kg/L
If ax2  bx  c  0 , then
x
b  b 2  4ac
2a
Equilibrium Constant [14.1]:
c
If aA + bB  cC + dD, then
Conjugate Pairs:
[C] [D]
d
 K eq
a
b
[A] [B]
K aKb  K w
pK a  pK b  pK w
Henderson–Hasselbalch [16.1]:
(Buffers)
C
n
pH  pK a  log b  pK a  log b
Ca
na
Atomic Weights (g/mol)
H = 1.01
P = 30.97
Li = 6.94
S = 32.01
C = 12.01
K = 39.10
N = 14.01
Cl = 35.45
O = 16.00
Ca = 40.08
F = 19.00
Br = 79.9
Na = 22.99
Ag = 107.87
Mg = 24.30
I = 126.90
CHEM 112, F'14 - Exam II
2/8a
1. Fill in each blank, indicating whether the species is an acid, a base or a spectator in the
reaction shown.
a) CH3CH2COOH(aq)
−
+ H2O(l) 
CH3CH2COO
_Acid___________
b) NH3 (aq)
+ H3O
−
+
(aq)
 NH4
−
(aq)
−
(aq)
(3 pts)
+ H2O(l)
(aq)
 HPO3
_ Base_________
_ Base___________
(aq)
2−
(aq)
(3 pts)
+ H3O
+
(aq)
_ Base__________
+H2PO3
e) cocaine(aq)
+
_ Acid__________
_ Acid___________
d) HCO3
+
+ H2O(l)  HPO3
(aq)
+ H3O
_Base__________
_ Base___________
c) H2PO3
(aq)
2−
(aq)
(3 pts)
+ H2CO3 (aq)
__ Base_________
+ H3O
+
−
(aq)
+ Cl
(aq)
 (cocaine·H)Cl(aq)
__Acid_______
(3 pts)
+ H2O(l)
(3 pts)
CHEM 112, F'14 - Exam II
2.
3/8a
A sample of benzoic acid [C6H5COOH] is dissolved in water and titrated with a 0.2304 M
solution of KOH. The equivalence point occurs when 48.35 mL of base has been added.
How many grams of benzoic acid were in the original sample? (15 pts)
CHEM 112, F'14 - Exam II
4/8a
3. How many moles of Na(CH3COO) do you need to add to 500 mL of 0.100 M CH3COOH
−5
(Ka = 1.810 ) to make a pH = 5.00 buffer? (15 pts)
CHEM 112, F'14 - Exam II
4. 50.00 mL of a 0.2500 M solution of pyridinium chloride [(C5H5NH)Cl] is titrated with
0.1500 M NaOH. [Hint: Pyridine (C5H5N) is a base.
a. What is the pH before any NaOH solution is added? (15 pts)
5/8a
CHEM 112, F'14 - Exam II
b. What is the pH after 50.00 mL of NaOH solution have been added?
6/8a
(15 pts)
CHEM 112, F'14 - Exam II
7/8a
5. 5.00 g of KBr and 1.00 g of HClO4 are dissolved in water to make 400 mL of solution. What
is the pH of the resulting solution? (15 pts)
CHEM 112, F'14 - Exam II
6. What is the pH of a 0.120 M solution of NH4Cl? (15 pts)
8/8a

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