Solution manual for MWH’s Water Treatment: Principles and Design Crittenden Trussell Hand Howe

Solution manual for
MWH’s Water
Treatment: Principles
and Design Crittenden
Trussell Hand Howe
Tchobanoglous 3rd
Edition

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PROBLEM 2-1
Problem Statement - Given the following test results, determine the mole fraction of
calcium (Ca2+).

Concentration, Concentration,
Cation mg/L Anion mg/L
Ca2+ 40.0 HCO3– 91.5
2–
Mg2+ 12.2 SO4 72
Na+ 15.1 Cl– 22.9
–
K+ 5.1 NO3 5.0


Solution
1. By definition, using Eq. 2-2, the mole fraction of Ca2+ is as follows.
n 2+
x Ca2+  Ca
n 2+  n 2+  n +  n +  nHCO -  n 2-  n -  n -
Ca Mg Na K 3 SO 4 Cl NO3




2. Substituting in the MW for each of the constituents yields the following:
40.08
xCa2+ 
40.08  24.31 22.99  39.1 61 96  35.45  62
40.08
  0.11
380.93


PROBLEM 2-2
Problem Statement - Determine the mole fraction of magnesium (Mg2+) for the water
given in Problem 2-1.

Solution
1. By definition, using Eq. 2-2, the mole fraction of Mg2+ is as follows.
n 2+
xMg2+  Mg
n 2+  n 2+  n +  n +  nHCO -  n 2-  n -  n -
Ca Mg Na K 3 SO 4 Cl NO3




2. Substituting in the MW for each of the constituents yields the following:

, 24.31
xMg2+ 
40.08  24.31 22.99  39.1 61 96  35.45  62
24.31
  0.06
380.93


PROBLEM 2-3
Problem Statement - Determine the mole fraction of sulfate (SO42–) for the water given
in Problem 2-1.

Solution
1. By definition, using Eq. 2-2, the mole fraction of SO2-4 is as follows:
n 2-

x SO2-  SO4
4 n
Ca
2+  nMg2+  nNa+  nK+  nHCO -  nCl-  nNO -
3 3




2. Substituting in the MW for each of the constituents yields the following:
96
xSO2- 
4 40.08  24.31 22.99  39.1 61 96  35.45  62
96
  0.25
280.93


PROBLEM 2-4
Problem Statement - Commercial-grade sulfuric acid is about 95 percent H2SO4 by
mass. If the specific gravity is 1.85, determine the molarity, mole fraction, and normality
of the sulfuric acid. Use Eq. 2-4 to determine molarity.

mass of solute, g
M, mole/L 
molecular weight of solute, g/molevolume of solution, L 
0.951.85
M, mole/L   0.0179 mole/L
98 1 
1. Use Eq. 2-2 to determine the mole fraction.