CIEG 135 Introduction to Environmental Engineering Fall, 2003
Assignment 3:
Due date: October 8th at beginning of class
Due: 10/8/03. Construct a pC-pH diagram for each of the following and use it to solve the
problem. If you want to solve directly by equation (optional), use it to confirm your graphical
answer.
If you are in need of any physical constants not given in the problem, it is your responsibility to
find a value and indicate its source in your homework. This is how it works in real life!
1. Trimethylamine, or TMA, is an odorous substance that exists in water in either a neutral form
- (CH3)3N - or a protonated form, (CH3)3NH+. The neutral form is much more volatile, i.e. it
readily separates into the gas phase (this is a general truism: charged species don't volatilize
easily).
Suppose the concentration of the positively charged form in water is 100 μg/L (this should
appear as a "mu" then a "g" for "micrograms" per liter) and the pH is 7. What is the
concentration of the neutral form under these conditions?
2. The same truism holds for hydrogen sulfide, H2S. If the total concentration of hydrogen
sulfide (including bisulfide) is 100 g/L, at what pH range is the neutral species at 1 g/L or
higher?
3. NH3 is toxic to fish at a concentration of 0.2 mg/L. To stay below this limit, what should be
the concentration limit for NTOTin water, at pH levels of 6, 7, 8, 9, and 10? (The non-charged
species NH3 passes across biological membranes more easily than does the charged species
NH4+.)
Note: NTOT is the sum of NH3 and NH4+.