CEE 680

23 October 2008

 

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

                    1015 joules = 1 crown joule

 

 

1.               (25%)  Calculate the pKa for the ammonia-ammonium ion system at 90°C.

 

 

2.               (65%) Determine the complete composition of a 1-liter volume of water to which you have added

a.      10-3 M of carbonic acid (H2CO3), and 10-2 M of sodium fluoride (NaF)

b.     10-3 M of sodium bicarbonate (NaHCO3), and 10-2.5 M of sodium monohydrogen 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.

 

Water has an unusually low boiling point based on its molecular weight.

b.

 

Mark Benjamin is the author of your textbook.

c.

 

Chemical potentials are independent of concentration

d.

 

Strong acids will almost completely donate their exchangeable hydrogen ions to the surrounding solvent molecules.

e.

 

Reactions with a large negative DG will always produce heat

f.

 

Sodium Acetate is not a strong base.

g.

 

Ionic strength affects the equilibria of acid/base reactions.

h.

 

Increases in ionic strength cause a decrease in the pKa of an acid, if the fully-protonated form of the acid is an uncharged species.

i.

 

The standard assumption used for calculating the pH of buffer solutions is that all positive ions are negligible.

j.

 

The value of ao plus a1 must always equal unity for a monoprotic acid.

 

 

 


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+  + 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

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

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