CEE 680 20 November 2008

# SECOND EXAM

Closed book, two pages of notes allowed.

# 1. Carbonate System.

(55% for both parts) Two raw drinking waters are mixed as they enter the headworks of a water treatment plant.  The two are characterized as follows:

 Water Flow (MGD) Alkalinity (mg/L as CaCO3) pH #1 20 25 6.50 #2 10 300 8.85

A. What will the pH of the blended water be immediately after mixing?

B. What will the pH of the blended water be after it has reached equilibrium with the bulk atmosphere?

C. How many mg/L of caustic soda (NaOH) must be added to the unequilibrated blended water in part “A” to raise the pH to 9.80 ?

# 2. Complexation

(45% for both parts) Aqueous fluoride forms strong complexes with many metals.  The following two part problem concerns complexes with Beryllium.

A.    (20%) Attached is an accurate graph of alpha values (vs log[ F-]) for the Beryllium-Fluoride system (equilibria data shown below).    Using this graph determine the complete species composition when the total Beryllium concentration is 0.10 mM and the total fluoride concentration is 0.40 mM.  Ignore the possible formation of any other complexes other than those from Be and F; also ignore any possible precipitation reactions.  Assume the water is a neutral pH.

B.    (20%) Describe in qualitative terms the impacts of pH on  this system.  Estimate in quantitative terms what the concentrations of each of the species would be if the pH were 2.2, instead of 7.0, and explain how you got these.

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) Citric acid C3H5O(COOH)3= H+  + C3H5O(COOH)2COO- 3.14 (&4.77,6.4) 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 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 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 Methane CH4 = H+ + CH3- 34