DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING; LAFAYETTE COLLEGE
Homework Assignment 4, Due Thurs, Sept 25
CE 321, Fall 2008
Note: this is the last HW Assignment before Exam 1
Davis and Masten Problem 2-22
DB1. A solution has 200 mg/L of sodium carbonate (Na2CO3). a) What is its molarity? b) Its
normality? c) What is the concentration in mg/L “as CaCO3”?
DB2. How much O2 (mg/L) is needed to oxidize 109 mg/L of glucose (C6H12O6) to CO2 and
water? (reaction given in your water chemistry review exercise in class)
DB3. Acetic acid has a pKa of 4.75. At a pH of 3, which is predominant, CH3COOH or
CH3COO-? How about at a pH of 6? At a pH of 4.75?
DB4. A water sample has a pH of 8.5, HCO3- concentration of 65 mg/L, and CO3-2
concentration of 15 mg/L. What is the alkalinity in mg/L as CaCO3?
DB5. What is the equilibrium concentration (mg/L) of CO2 in water at 20 °C and 1 atm of
pressure? The concentration of CO2 in the atmosphere is currently 385 ppm (by volume).
DB6. The gas above the liquid in a 10°C can of Coke is pure CO2 at a pressure of 2 atm. What is
the pH of the Coke?
Here are two reactions you’ll need:
322
)(
2COHOHCO aq
⇔
+ K=10-2.8
−
++⇔ 332 HCOHCOH K
A1=10-6.3
Hints: 1) the Coke is acidic; 2) the only ions in the system are H+, OH- and HCO3-, 3) the Coke
must satisfy electroneutrality, i.e. the sum of the cation charges must equal the sum of the anion
charges
DB7. A common carbonate rock in the Lehigh Valley and Bushkill Creek watershed is dolomite
CaMg(CO3)2 The Ca+2 concentration in the lower Bushkill Creek is 50 mg/L (range 20 - 70),
Mg+2 is 25 mg/L (range 10 - 50), the pH is 7.5, and the bicarbonate is 125 mg/L. Is the solution
oversaturated, undersaturated, or saturated with respect to dolomite? Given the ranges of
concentrations, is it likely that the stream switch from undersaturated to oversaturated?
