CEE 370

Spring 2001

Exam #1

 

March 15, 2001

 

Closed Book, one sheet of notes allowed

Please answer any 5 of the following 13 questions.  Each is worth 20 points.  Show all work.  Be neat, and box-in your answer.

 

 

 

1.      Calculate the ThOD of the following wastewaters in mg/L: (20 points)

a.      10-3 moles/L of dodecane, C12H26

 

The balanced stoichiometric equation is:

The ThOD is then:

 

 

b.      3x10-3 moles/L of oxalic acid, C2H2O4

 

The balanced stoichiometric equation is:

The ThOD is then:

 

 

 

2. Calculate the concentration of the following solutions as mg-Carbon/L and tell which family of organic compounds each comes from: (20 points)

a.      10-3 moles/L of hexane, C6H8

 

 

Hexane is a member of the Alkane family.

 

b.      3x10-3 moles/L of oxalic acid, C2H2O4

 

 

Oxalic Acid is a member of the Carboxylic Acid family.

 

c.      30 mg-ethanol/L, CH3CH2OH

 

 

Ethanol is a member of the Alcohol family.

 

 


3. Short Answer (20 points)

a.      What distinguishes a carboxylic acid from other chemical substances? (5 points)

 

 

b.      Explain what pseudo first order means. (5 points)

 

Due to an excess of one or more reactants, the reaction rate is proportional to the concentration of only one of the reactants

 

c.      Why does ozone form in the upper atmosphere? (5 points)

 

Light of low wavelength (thus, high energy) strikes oxygen in the upper atmosphere to form ozone.  This high energy light does not substantially penetrate into the lower atmosphere.

 

d.      What is the difference between partitioning and adsorption? (5 points)

 

Partitioning occurs where a pollutant separates from the dissolved state to a state where it is associated with a particle or solid surface.  The nature of this association may be either a direct link to the solid surface (adsorption) or dissolution into an organic layer attached to the surface.

 


 

 

 

4. Perform a charge balance on the following water.  As part of this balance determine the amount of unbalanced charge and its percentage of the total.  What does this number tell you about the accuracy of the chemical analysis? (20 points)

Chemical Substance

Conc. (mg/L)

GFW

Conc. (mM)

Conc. (meq/L)

Na+

31.2

22.9898

1.3571236

1.3571236

K+

1.5

39.0983

0.0383648

0.0383648

Ca+2

42.8

40.08

1.0678643

2.1357285

Mg+2

3.5

24.305

0.1440033

0.2880066

NO3-

8.8

62.0049

0.1419243

0.1419243

SO4-2

14.6

96.0576

0.1519921

0.3039843

Cl-

37.2

35.453

1.0492765

1.0492765

HCO3-

59.3

61.0171

0.9718587

0.9718587

 

cations =

3.81922356

anions =

2.46704376

 

 

% diff. =

35.40%

 

This tells us that there is a substantial error.  Either the cations are over estimated, the anions are underestimated or there is a major anion that was omitted.

 


 

5. What is the TDS (in mg/L), the total hardness (in mg/L as CaCO3) and the total alkalinity (in mg/L as CaCO3) for the water in question #4? (20 points)

 

 

Chemical Substance

Conc. (mg/L)

 

Na+

31.2

 

K+

1.5

 

Ca+2

42.8

 

Mg+2

3.5

 

NO3-

8.8

 

SO4-2

14.6

 

Cl-

37.2

 

HCO3-

59.3

 

 

Sum  =

198.9

 mg/L

 

or

Sum  =

139.6

 mg/L

with loss of CO2

 


 

6. What is the ionic strength for the water in question #4? (20 points)

 

 

Chemical Substance

Conc. (mg/L)

GFW

Conc. (mM)

Conc. (meq/L)

z

z^2

cz^2 (M)

Na+

31.2

22.9898

1.3571236

1.3571236

1

1

0.001357

K+

1.5

39.0983

0.0383648

0.0383648

1

1

3.84E-05

Ca+2

42.8

40.08

1.0678643

2.1357285

2

4

0.004271

Mg+2

3.5

24.305

0.1440033

0.2880066

2

4

0.000576

NO3-

8.8

62.0049

0.1419243

0.1419243

1

1

0.000142

SO4-2

14.6

96.0576

0.1519921

0.3039843

2

4

0.000608

Cl-

37.2

35.453

1.0492765

1.0492765

1

1

0.001049

HCO3-

59.3

61.0171

0.9718587

0.9718587

1

1

0.000972

 

 

 

 

 

 

 

0.5*Sum =

0.004507

 


 

7. Determine the TDS value in mg/L based on the following analysis.  Four hundred milliliters of a water sample are filtered though a glass fiber filter.  The filter paper is dried to a constant weight (1.4569 g).  Two hundred fifty milliliters of the filtrate are added to an evaporating dish.  The tare for this dish was 24.5087 g.  The dish and water are placed in a drying oven and removed after all of the water is gone.  Once it has returned to room temperature, the dish is re-weighed and found to be 24.8904 g. (20 points)

 

 

 

 

 

 

8. True/False.  Indicate whether the following statements are true (T) or false (F).  (20 points total; 2 points each)

 

1.

T

A 1N concentration is the same as 1 equivalent/L

2.

F

A water having 100 mg/L of hardness as CaCO3 may also be said to have 10 moles/L of hardness

3.

T

The activity coefficient usually goes down as ionic strength goes up.

4.

F

A first order reaction is almost always slower that a second order reaction

5.

T

Catalysts accelerate chemical reactions by lowering the activation energy

6.

F

When Gibbs Free Energy increases, the reaction will tend to go forward

7.

F

Alkenes all have triple bonds

8.

T

Henry’s law describes the relationship between partial pressure and dissolved concentration

9.

T

As the organic content of a sediment increases, its ability to accumulate organic contaminants by partitioning increases

10.

F

TSS is always greater than TDS

 


 

 

9. Use the following data to estimate the rate constant for the reaction between A and B at 40°C  (20 points)

 

Temperature

Rate constant

20°C

3.6 M-1s-1

50°C

56.2 M-1s-1

 

Best to use the Arrhenius Equation:

so then:

 

 

10. The half life for toluene in groundwater is estimated to be 12 days.  If the concentration of toluene in a groundwater plume is currently 48 ppb, what will the concentration be 30 days from now?  (20 points)

 

so:

 

 

 

11.  The equilibrium constant for the following reaction is 10-12.3.  What percent of the total phosphate is in the form of HPO4-2 at pH 13?  (20 points)

 

HPO4-2 = PO4-3 + H+

 

 

 

 

 

 

 

 


12. You’ve added 10-4 moles of sodium carbonate to a liter of water.  List all possible species and write the necessary equations (equilibrium, mass balance, electroneutrality) to solve this chemical system  (20 points)

 

Species:

  1. Na+
  2. CO3-2
  3. HCO3-
  4. H2CO3
  5. H+
  6. OH-

 

Equations:

 

  1. Kw=[OH-][H+]
  2. K1 = [H+][HCO3-]/[ H2CO3]
  3. K2 = [H+][CO3-2]/[ HCO3-]
  4. Ct = [Na+] = [H2CO3] + [HCO3-] + [CO3-2]
  5. [Na+] + [H+] = [HCO3-] + 2[CO3-2]

 

13. You need to oxidize nitrite (NO2-) to nitrate (NO3-) by addition of potassium permanganate (KMnO4).  After the reaction is complete, the manganese is reduced to manganese dioxide (MnO2).  How many mg/L of permanganate are needed to completely oxidize 4.6 mg/L of nitrite? (20 points).

 

First, you must balance the REDOX equation to get the stoichiometry.  This requires that the oxidation states for N and Mn be determined, and the electrons be balanced, then balance all non-H/O atoms, finally balance the O atoms with water as needed, and the H with the proton as needed.

 

now calculate:

 

 

 


Appendix

 

Selected Chemical Constants

Element

Symbol

Atomic #

Atomic Wt.

Valence

Electronegativity

Aluminum

Al

13

 26.98

3

1.47

Boron

B

 5

 10.81

3

2.01

Calcium

Ca

20

 40.08

2

1.04

Carbon

C

 6

 12.01

2,4

2.50

Cerium

Ce

58

140.12

3,4

1.06

Helium 

He

 2

  4.00

0

 

Holmiuum

Ho

67

164.93

3

1.10

Hydrogen

H

 1

  1.01

1

2.20

Magnesium

Mg

12

 24.31

2

1.23

Manganese

Mn

25

 54.94

2,3,4,6,7

1.60

Osmium  

Os

76

190.2

2,3,4,8

1.52

Oxygen  

O

 8

16.00

2

3.50

Potassium

K

19

 39.10

1

0.91

Sodium  

Na

11

 22.99

1

1.01

Sulfur  

S

16

 32.06

2,4,6

2.44

 

 

Selected Acidity Constants  (Aqueous Solution, 25°C, I = 0)

   NAME

   FORMULA

 pKa

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               

Bisulfate ion

HSO4- = H+ + SO4-2

 2

Phosphoric acid

H3PO4 = H+ + H2PO4-

 2.15 (&7.2,12.3)

Hydrofluoric acid

HF = H+  + F-

 3.2

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

Ammonium ion

NH4+ = H+  + NH3

 9.24

Hydrocyanic acid

HCN = H+  + CN-

 9.3

Phenol

C6H5OH = H+  + C6H5O-

 9.9

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