CEE
680
|
17 October 2007 |
FIRST EXAM
Closed book, one page of
notes allowed.
Answer
all questions. Please state any
additional assumptions you made, and show all work. You are welcome to use a graphical method of
solution if it is appropriate.
Miscellaneous Information:
R = 1.987 cal/mole°K = 8.314 J/mole°K
Absolute zero = -273.15°C
1 joule = 0.239 calories
1 parsec = 19,173,511,600,000 miles
1. (50%) What is the pH of a 10-2 M solution of Sodium Nitrite (NaNO2) to which you have added 5 x 10-3 M Nitric Acid (HNO3)? Calculate this for each of the three conditions below (obviously the ionic strength will never be zero for this solution, but let’s assume that ideal case for part “a” and “b”, anyway).
a. 25°C, I = 0
b. 1°C, I = 0
c. 25°C, I = 0.10
2. (40%) What is the complete composition of a 1-liter volume of water to which you have added 10-2 M of ammonium acetate (NH4CH3CO2)? Approximate values (± 0.2 log units) will suffice.
3. (10%) True/False. Mark each one of the following statements with either a "T" or an "F".
a. ______ Solutions of pure compounds exhibit
their highest buffer intensities at pHs near the compound’s pKa .
b. ______ Solutions of hydrochloric acid are always lower in pH
than solutions of acetic acid.
c. ______ A 10-2 F solution of HCl has a pH of about 2.
d. ______ Strong acids will always have
strong conjugate bases.
e. ______ The sum of alkalinity and acidity
equals twice the total inorganic carbon.
f. ______ Dihydrogen
phosphate (H2PO4-) is an amphoteric
substance.
g. ______ The buffer intensity of a solution is
the inverse of the alkalinity.
h. ______ Positive DH values indicate that the
reaction is not spontaneous
i. ______ The standard assumption used for
calculating the pH of an acidic solution is that the [OH-] is
negligible.
j. ______ For a diprotic
acid, the value of ao plus a1 must always equal one.
Selected
Acidity Constants (Aqueous
Solution, 25°C, I = 0)
|
NAME |
FORMULA |
pKa |
|
|
Perchloric acid |
HClO4 = H+ +
ClO4- |
-7 STRONG |
|
|
Hydrochloric acid |
HCl = H+ + Cl- |
-3 |
|
|
Sulfuric acid |
H2SO4= H+ + HSO4- |
-3 (&2) ACIDS |
|
|
Nitric acid |
HNO3 = H+ + NO3- |
-0 |
|
|
Hydronium ion |
H3O+ = H+ + H2O |
0 |
|
|
Trichloroacetic acid |
CCl3COOH = H+ + CCl3COO- |
0.70 |
|
|
Iodic acid |
HIO3 = H+ + IO3- |
0.8 |
|
|
Bisulfate ion |
HSO4- = H+ +
SO4-2 |
2 |
|
|
Phosphoric acid |
H3PO4 = H+ + H2PO4- |
2.15 (&7.2,12.3) |
|
|
o-Phthalic acid |
C6H4(COOH)2 = H+ + C6H4(COOH)COO- |
2.89 (&5.51) |
|
|
Citric acid |
C3H5O(COOH)3=
H+ + C3H5O(COOH)2COO- |
3.14 (&4.77,6.4) |
|
|
Hydrofluoric acid |
HF = H+
+ F- |
3.2 |
|
|
Aspartic acid |
C2H6N(COOH)2= H+ + C2H6N(COOH)COO- |
3.86 (&9.82) |
|
|
m-Hydroxybenzoic acid |
C6H4(OH)COOH = H+ + C6H4(OH)COO- |
4.06 (&9.92) |
|
|
p-Hydroxybenzoic acid |
C6H4(OH)COOH = H+ + C6H4(OH)COO- |
4.48 (&9.32) |
|
|
Nitrous acid |
HNO2 = H+ + NO2- |
4.5 |
|
|
Acetic acid |
CH3COOH = H+ + CH3COO- |
4.75 |
|
|
Propionic acid |
C2H5COOH = H+ + C2H5COO- |
4.87 |
|
|
Carbonic acid |
H2CO3 = H+ + HCO3- |
6.35 (&10.33) |
|
|
Hydrogen sulfide |
H2S = H+ + HS- |
7.02 (&13.9) |
|
|
Dihydrogen phosphate |
H2PO4- = H+ + HPO4-2 |
7.2 |
|
|
Hypochlorous acid |
HOCl = H+ + OCl- |
7.5 |
|
|
Boric acid |
B(OH)3 + H2O = H+ + B(OH)4- |
9.2 (&12.7,13.8) |
|
|
Ammonium ion |
NH4+ = H+ + NH3 |
9.24 |
|
|
Hydrocyanic acid |
HCN = H+
+ CN- |
9.3 |
|
|
p-Hydroxybenzoic acid |
C6H4(OH)COO- = H+ + C6H4(O)COO-2 |
9.32 |
|
|
Phenol |
C6H5OH = H+ + C6H5O- |
9.9 |
|
|
m-Hydroxybenzoic acid |
C6H4(OH)COO- = H+ + C6H4(O)COO-2 |
9.92 |
|
|
Bicarbonate ion |
HCO3- = H+ + CO3-2 |
10.33 |
|
|
Monohydrogen phosphate |
HPO4-2 = H+ + PO4-3 |
12.3 |
|
|
Bisulfide ion |
HS- = H+ + S-2 |
13.9 |
|
|
Water |
H2O = H+ + |
14.00 |
|
|
Ammonia |
NH3 = H+ + NH2- |
23 |
|
|
Methane |
CH4 = H+ + CH3- |
34 |
|
|
Species |
kcal/mole |
kcal/mole |
|
Ca+2(aq) |
‑129.77 |
‑132.18 |
|
CaC03(s), calcite |
‑288.45 |
‑269.78 |
|
CaO (s) |
‑151.9 |
‑144.4 |
|
C(s), graphite |
0 |
0 |
|
CO2(g) |
‑94.05 |
‑94.26 |
|
CO2(aq) |
‑98.69 |
‑92.31 |
|
CH4 (g) |
‑17.889 |
‑12.140 |
|
H2CO3 (aq) |
‑167.0 |
‑149.00 |
|
HCO3- (aq) |
‑165.18 |
‑140.31 |
|
CO3-2 (aq) |
‑161.63 |
‑126.22 |
|
CH3COO-, acetate |
‑116.84 |
‑89.0 |
|
H+ (aq) |
0 |
0 |
|
H2 (g) |
0 |
0 |
|
HF (aq) |
-77.23 |
-71.63 |
|
F- (aq) |
-80.15 |
-67.28 |
|
Fe+2 (aq) |
‑21.0 |
‑20.30 |
|
Fe+3 (aq) |
‑11.4 |
‑2.52 |
|
NO2- (aq) |
‑25.00 |
‑8.89 |
|
NO3- (aq) |
‑49.372 |
‑26.43 |
|
NH3 (g) |
‑11.04 |
‑3.976 |
|
NH3 (aq) |
‑19.32 |
‑6.37 |
|
NH4+ (aq) |
‑31.74 |
‑19.00 |
|
HNO2 (aq) |
‑28.49 |
‑10.27 |
|
HNO3 (aq) |
‑49.372 |
‑26.41 |
|
O2 (aq) |
‑3.9 |
3.93 |
|
O2 (g) |
0 |
0 |
|
|
‑54.957 |
‑37.595 |
|
H2O (g) |
‑57.7979 |
‑54.6357 |
|
H2O (l) |
‑68.3174 |
‑56.690 |
|
PO4-3 (aq) |
-305.30 |
-243.50 |
|
HPO4-2 (aq) |
-308.81 |
-260.34 |
|
H2PO4- (aq) |
-309.82 |
-270.17 |
|
H3PO4 (aq) |
-307.90 |
-273.08 |
|
SO4-2 |
‑216.90 |
‑177.34 |
|
HS- (aq) |
‑4.22 |
3.01 |
|
H2S(g) |
‑4.815 |
‑7.892 |
|
H2S(aq) |
‑9.4 |
‑6.54 |
