ENCE 433 Dr. Alba Torrents

ENVIRONMENTAL ENGINEERING ANALYSIS Fall 1996

Homework Set # 8 Out: December 3 Due: December 10

REDOX

  1. What is the oxidation state of (a) Mn in MnO4-, (b) C in CCl4, (c) Cr in Cr2O7-2, (d) Cl in KClO, (e) C in CH3OH, and (f) C in CN- ?


2. Dechlorination is the practice of removing the total combined chlorine residual that exists after chlorination, with the objective to reduce the toxic effects of chlorinated effluents on receiving-stream biota. In water treatment plants, sulfur dioxide (SO2) is often used to reduce free chlorine (HOCl) and chloroamine compounds. In both reactions, sulfur dioxide forms sulfate and the residual chlorine compounds form chloride (Cl-).

  1. which compound(s) is (are) the oxidant(s)
  2. which compounds get oxidize
  3. Write the two balanced reactions


  1. Estimate the EH for the aquatic habitats characterized by the following analytical information at 25oC. Which one is the most reducing habitat?

  1. An anaerobic digestor in which 65 % CH4 and 35% CO2 are in contact with water at pH = 7.0.
  2. A water sample at pH = 6.0, containing [SO4-2] = 10-3M and smelling of H2S (consider PH2S = 10-8 atm).
  3. Water from the deeper layers of a lake having a dissolved O2 concentration of 0.03 mg/L and a pH of 7.0.

1/8 SO4-2 + 5/4 H+ + e- 1/8 H2S (g) + ½ H2O peo = 5.25

¼ O2 + H+ + e- ½ H2O peo = 20.75

1/8 CO2 (g) + H+ + e- 1/8 CH4 (g) + ¼ H2O peo = 2.87

EoH = 2.3 RT/F peo (R=1.98; F=23,062)

4. Will permanganate ion oxidize bromide ion when all concentrations are 1M ?

Eo(volt) MnO4-2 /Mn+2 = 1.49; Eo(volt) Br2 / Br- = 1.09