CEE 680

7 October 1999

 

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/moleK = 8.314 J/moleK

Absolute zero = -273.15C

1 joule = 0.239 calories

1015 newtons = 1 figanewton

 

 

 

 

1.                  (50%) What is the pH of a 0.05 F solution of Sodium Sulfide (Na2S) to which you have added 0.09 M of HCl ? (Ignore ionic strength effects)

 

a. 25C

b. 100C.

 

 

 

2.                  (40%) What is the complete composition of a 1 liter volume of water to which you have added 10-3 M of ammonium nitrate (NH4NO3) and 10-4 M of disodium hydrogen phosphate (Na2HPO4) ? 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. ______ The pH of a solution of a strong acid is always equal to its pC.

 

b. ______ Free protons generally dont exist in aqueous solution.

 

c. ______ Buffer intensity is a measure of the degree to which a solution resists change in pH

 

d. ______ A solution with a very high acid neutralizing capacity will necessarily have a very high buffer intensity as well.

 

e. ______ Reactions with a large negative DG will proceed very quickly toward the right.

 

f. ______ Acetic Acid is not a strong acid.

 

g. ______ Strong acids have strong conjugate bases.

 

h. ______ The pH of a solution prepared from an equimolar concentration of a weak acid and its conjugate base is approximately equal to the pC.

 

i. ______ One can usually assume that the protonated form (i.e., acid form) is negligible compared to the deprotonated form when a salt (i.e., conjugate base) of a simple monoprotic acid is added to water.

 

j. ______ The value of ao can only exceed a value of 1.00 at pHs far below the pKa.

 

 

 


Selected Acidity Constants (Aqueous Solution, 25C, 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+ + OH-

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

Fe+2 (aq)

‑21.0

‑20.30

Fe+3 (aq)

‑11.4

‑2.52

Fe(OH)3 (s)

‑197.0

‑166.0

Mn+2 (aq)

‑53.3

‑54.4

MnO2 (s)

‑124.2

‑111.1

Mg+2 (aq)

‑110.41

‑108.99

Mg(OH)2 (s)

‑221.00

‑199.27

NO3- (aq)

‑49.372

‑26.43

NH3 (g)

‑11.04

‑3.976

NH3 (aq)

‑19.32

‑6.37

NH4+ (aq)

‑31.74

‑19.00

HNO3 (aq)

‑49.372

‑26.41

O2 (aq)

‑3.9

3.93

O2 (g)

0

0

OH- (aq)

‑54.957

‑37.595

H2O (g)

‑57.7979

‑54.6357

H2O (l)

‑68.3174

‑56.690

SO4-2

‑216.90

‑177.34

HS- (aq)

‑4.22

3.01

H2S(g)

‑4.815

‑7.892

H2S(aq)

‑9.4

‑6.54