CHEM 2A – FINAL EXAM 1

CHEM 2A – FINAL EXAM
First letter of your last name
NAME:___________________________
PERM#____________________
INSTRUCTIONS: Fill in your name, perm number and first initial of your last name above. Be sure to
show all of your work for full credit. Use the back of the page if necessary.
Useful information (periodic table, equations, constants etc..) is at the end of the test packet. You may
tear them off for easy reference.
1

CHEM 2A – FINAL EXAM
SCORE: ________ 200 pts possible
PART I – SHORT RESPONSE / MULTIPLE CHOICE
1. (12 pts) Consider the following generalized reaction and answer the following
questions.
forward
( g )
2
( g) 2
reverse ( l)
A + B C
A) When the above system is at equilibrium which of the following statements is true
concerning the reaction rates
a) The forward rate of reaction is faster than the reverse rate of reaction
b) The reverse rate of reaction is faster than the forward rate of reaction
c) The forward rate of reaction is equal to the reverse rate of reaction
d) There is not enough information to answer the question
B) If additional component B is added to the system at equilibrium which of the
following statements is true regarding the reaction quotient Q before equilibrium is
reestablished
a) The value of Q is greater then K
b) The value of Q is less than K
c) The value of Q is the same as K
c) There is not enough information to answer the question
C) If the pressure of the system is decreased by increasing the volume of the container
which of the following statements is true
a) The reaction shifts to the right
b) The reaction shifts to the left
c) There is no change
d) There is not enough information to answer the question
2. (10 pts) Write the molecular formulas for the following compounds
A) Sodium acetate ___________________
B) Potassium dihydrogen phosphate ___________________
C) Ammonium sulfate ___________________
D) Ferric oxide ___________________
E) Zinc sulfide ___________________
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CHEM 2A – FINAL EXAM
3. (10 pts) Will the following solutions be acidic, basic or neutral
A) 0.10 M ammonium chloride _________________
B) 0.05 M calcium bromide _________________
C) 0.32 M citric Acid _________________
D) 0.87 M pyridine _________________
E) 0.1 M sodium acetate, 0.1 M acetic acid _________________
4. (6 pts) The sodium salt of a weak acid, NaA, is dissolved in water. No other substance
is added. Which of the following statements is true
A) [H + ] = [A - ]
B) [H + ] = [OH - ]
C) [OH - ] = [A - ]
D) [HA] = [OH - ]
E) none of the above
5. (6 pts) Which of the following is true. The value of the equilibrium constant, K, is
dependent on
I. The temperature of the system
II. The nature of the reactants and products
III. The concentration of reactants
IV. The concentration of products
A) I and II
B) III and IV
C) II and III
D) II, III and IV
E) None of the above
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CHEM 2A – FINAL EXAM
6. (6 pts) Which of the following solutions would be the best system if a buffer near pH
3.7 was desired
A) 0.1 M acetic acid, 0.1 M acetate
B) 0.1 M benzoic acid, 0.1 M benzoate
C) 0.1 M formic acid, 0.1 M formate
D) 0.1 M hydrofluoric acid, 0.1 M fluoride
E) 0.1 M nitrous acid, 0.1 M nitrite
7. (8 pts) Write each answer with the correct number of significant figures
A) 1.021 + 2.69 =
B) 12.3 - 1.63 =
C) 4.34 × 9.2 =
D) 0.0602 ÷ (2.113 × 10 -4 ) =
PART II – CALCULATIONS
8. (12 pts) A 1.621 gram sample of an unknown organic compound containing C,H and O
only was combusted in the presence of an excess of oxygen gas. Analysis of the products
revealed that 1.902 grams of water and 3.095 grams of carbon dioxide were produced.
What is the empirical formula of the compound
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CHEM 2A – FINAL EXAM
9. (10 pts) Calculate the volume of carbon dioxide at 25 o C and 1 atm needed for a plant
to photosynthesize 1.0 gram of glucose, C 6 H 12 O 6 , by the following reaction:
6CO + 6H O → C H O + 6O g
2( g ) 2 ( l) 6 12 6( s) 2( )
10. (12 pts) Balance the following redox reaction of oxalic acid and permanganate ion in
acidic solution.
HCO + MnO → CO + Mn
− 2+
2 2 4( aq) 4( aq) 2( g ) ( aq)
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CHEM 2A – FINAL EXAM
11. (16 pts) Nitrogen gas, N 2 reacts with hydrogen gas, H 2 to form ammonia gas, NH 3 in
the presence of a proper catalyst. The following apparatus is constructed in a lab with
room temperature of 23 o C.
Flask A contains 1.25 L of nitrogen gas at a pressure of 1.1 atm. Flask B contains 3.5 L
of hydrogen at a pressure of 0.75 atm.
A) Write the balanced chemical equation for the reaction of hydrogen and nitrogen to
form ammonia.
B) Calculate the total pressure in the apparatus when the stopcock is opened and before
any reaction occurs (assume the stopcock has no volume).
C) How many moles of ammonia are formed
D) Calculate the partial pressures of all the gasses remaining after the reaction has gone
to completion.
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CHEM 2A – FINAL EXAM
12. (12 pts) Calcium carbide, CaC 2 , reacts with water to form calcium hydroxide and the
flammable gas acetylene, C 2 H 2 . This reaction was once used for lamps on bicycles and
miner’s hats because the reactants are easy to transport. The chemical equation is:
CaC + 2 H O → Ca( OH ) + C H
g
2( s) 2 ( l) 2( aq) 2 2( )
A) What is the limiting reagent if 100 grams of water are reacted with 100 grams of
calcium carbide
B) What mass of acetylene is produced
C) What mass of the excess reactant remains after the reaction is complete
13. (10 pts) Mass spectrometry analysis of copper metal reveals that 69.09% of the
sample is 63 Cu (62.93 amu/atom) the only other isotope in this sample was 65 Cu. Using
the atomic mass of copper (63.55 g/mole) determine the mass of 65 Cu in amu.
Note: 1 gram = 6.022 × 10 23 amu.
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CHEM 2A – FINAL EXAM
14. (12pts) Calculate the pH of 50 mL of a 0.10 M HF solution that has been titrated with
15 mL of 0.25 M KOH.
15. (12 pts)The K sp for PbI 2 in water is 1.4 × 10 -8 . What is the concentration of Pb 2+ in a
saturated solution of PbI 2
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CHEM 2A – FINAL EXAM
16. (20 pts) Consider the titration of 50 mL of 0.05 M malonic acid with 0.1 M KOH.
The titration curve is shown below.
A) Label the first and second equivalence points on the plot above
B) How many mL of KOH must be added to result in a solution with a pH of 2.82
C) Calculate the pH of the solution when 45 mL of KOH have been added
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CHEM 2A – FINAL EXAM
17. (14 pts) Ferric hydroxide, Fe(OH) 3 is minutely soluble in water (K sp = 4 × 10 -38 ).
What is the concentration of Fe 3+ in a pH 5.0 buffer solution that is saturated with
Fe(OH) 3
18. (12 pts) A 1.4922 ± 0.0002 gram sample of silver ore was digested in acid and the
silver was precipitated as silver chloride, AgCl. The solid silver chloride weighed
0.0892 ± .0002 grams. Calculate the mass percent of silver in the ore. Report your result
with the correct significant figures and absolute error.
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CHEM 2A – FINAL EXAM
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CHEM 2A – FINAL EXAM
Equations
x =
∑
[ X ]
i
[ ] + [ ]
f
i
n
f
x
I
X
=
S X I +
i
X
S
s =
∑
i
( x
i
− x)
n −1
[ X] = [ X]
f
[ S] = [ S]
f
i
i
2
( V0
)
( V )
( VS
)
( V )
N
0
μ =
x ±
ts
n
= 6.02214×
10
23
−27
amu = 1.66054×
10 kg
R
R
X S
2 2
= F
e= [ X ] [ S]
( e1) + ( e2) + ( e3)
% % % % ...
2 e= e 2 + e 2 + e 2
...
1 2 3
N
0
= 6.02214×
10
23
−27
amu = 1.66054×
10 kg
PV
= nRT
kB
= 1.38066×
10
JK
−23 −1
R = 0.08206 Latmmol K
R=
8.31451 J mol K
−1 −1
−1 −1
P = P + P + P +⋅⋅⋅
Total
P = χ × P
1 1
1 2 3
aA + bB cC + dD
3RT
2RT
8RT
u = rms
; ump ; uavg
M = M = π M
[ ] c
[ ] d
C D
K =
a b
[ A] [ B]
2
⎡ ⎛ n ⎞ ⎤
⎢Pobs
+ a⎜
⎟ ⎥( V − nb)
= nR
⎢⎣
⎝V
⎠ ⎥⎦
Total
pH + pOH = pK
w
T
14
Kw
= [ H + ][ OH
− ] = 1×
10
−
Kp
n
χ
1
=
n
1
Total
= K( RT) Δn
pK + pK = pK
a b w
( conjugate pairs)
1 torr = 1 mmHg 760 mm Hg = 1 atm
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CHEM 2A – FINAL EXAM
Acid Dissociation Constants (25 o C)
Name Formula K a1 K a2 K a3
Acetic HC 2 H 3 O 2 1.8 × 10 -5
Ammonium ion
+
NH 4 5.6 × 10 -10
Arsenic H 3 AsO 4 5.6 × 10 -3 1.0 × 10 -7 3.9 × 10 -12
Ascorbic HC 6 H 7 O 6 8.0 × 10 -5 1.6 × 10 -12
Benzoic HC 7 H 5 O 2 6.5 × 10 -5
Boric H 3 BO 3 5.8 × 10 -10
Carbonic H 2 CO 3 4.3 × 10 -7 4.8 × 10 -11
Chloroacetic HC 2 H 2 O 2 Cl 1.4 × 10 -3
Citric H 3 C 6 H 5 O 7 7.4 × 10 -4 1.7 × 10 -5 4.1 × 10 -7
Formic HCHO 2 1.8 × 10 -4
Hydrocyanic HCN 4.9 × 10 -10
Hydrofluoric HF 7.2 × 10 -4
Hydrogen selenate ion
-
HSeO 4 2.2 × 10 -2
Hydrogen sulfide H 2 S 9.1 × 10 -8 1.1 × 10 -12
Hypobromous HBrO 2.1 × 10 -9
Hypochlorous HClO 3.0 × 10 -8
Hypoiodous HIO 2.3 × 10 -11
Iodic HIO 3 1.7 × 10 -1
Lactic HC 3 H 5 O 3 1.4 × 10 -4
Malonic H 2 C 3 H 2 O 4 1.5 × 10 -3 2.0 × 10 -6
Nitrous HNO 2 4.5 × 10 -4
Oxalic H 2 C 2 O 4 5.9 × 10 -2 6.4 × 10 -5
Phenol HC 6 H 5 O 1.3 × 10 -10
Phosphoric H 3 PO 4 7.5 × 10 -3 6.2 × 10 -8 4.2 × 10 -13
Propionic HC 3 H 5 O 2 1.3 × 10 -5
Pyrophosphoric H 4 P 2 O 7 3.0 × 10 -2 4.4 × 10 -3
Selenous H 2 SeO 3 2.3 × 10 -3 5.3 × 10 -9
Sulfuric H 2 SO 4 Strong Acid 1.2 × 10 -2
Sulfurous H 2 SO 3 1.7 × 10 -2 6.4 × 10 -8
Tartaric H 2 C 4 H 4 O 6 1.0 × 10 -3 4.6 × 10 -5
Base Dissociation Constants (25 o C)
Name Formula K b
Ammonia NH 3 1.8 × 10 -5
Aniline C 6 H 5 NH 2 4.3 × 10 -10
Dimethlyamine (CH 3 ) 2 NH 5.4 × 10 -4
Ethylamine C 2 H 5 NH 2 6.4 × 10 -4
Hydrazine H 2 NNH 2 1.3 × 10 -6
Hydroxylamine HONH 2 1.1 × 10 -8
Methylamine CH 3 NH 2 4.4 × 10 -4
Pyridine C 5 H 5 N 1.7 × 10 -9
Trimethylamine (CH 3 )CN 6.4 × 10 -5 13