ENVIRONMENTAL ENGINEERING ANALYSIS Fall 1996

Homework Set # 4 Out: October 15 Due: October 24

Carbonate system and alkalinity

1. The average pressure of CO2 in the air is 3.0x10-4 atm. Calculate the pH of water in equilibrium with the air at 25oC, and the concentration of all species present in this solution.

2. A sample of water from the overflow of the recarbonation basin that follows a precipitation/softening process has a pH of 9.0; 200 mL of water require 1.1 mL of 0.02 N H₂SO₄ to titrate it to the phenolphthalein endpoint (carbonate alkalinity) and 22.9 ml of 0.02 N H₂SO₄ to titrate it further to the methyl orange endpoint (total alkalinity). Assuming the sample contains no calcite particles, what are the total carbonate alkalinities of the sample in meq/L and the total alkalinity in mg/L as CaCO₃ ?

3. Water from a deep well is found to have a pH of 6.3 and an alkalinity of 1.00x10-3 equivalents/l

a. Calculate CT for this well water prior to equilibration with atmospheric CO2

b. Calculate the pH and CT after equilibration with atmospheric CO2