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Class CEE 350 Quiz #4
A groundwater contains 80 mg/L Ca
2+
and 45 mg/L Mg
2+
. Find the total
hardness expressed in mg/L as CaCO
3
.
The atomic weights of calcium and
magnesium are 40 and 24.3 g/mol, respectively.
The concentrations of Ca
2+
and Mg
2+
expressed in different units are shown
below.
±²
±²
±²
±²
L
meq
mg
meq
L
mg
EW
C
L
meq
Ca
Ca
Ca
/
00
.
4
/
20
/
80
/
±²
±²
±²
±²
L
meq
mg
meq
L
mg
EW
C
L
meq
Mg
Mg
Mg
/
69
.
3
/
2
.
12
/
45
/
±²
±²
L
mg
EW
EW
C
CaCO
as
L
mg
Ca
CaCO
Ca
Ca
/
200
50
0
.
4
_
_
/
3
3
u
±²
±²
L
mg
EW
EW
C
CaCO
as
L
mg
Mg
CaCO
mg
mg
/
184
50
69
.
3
_
_
/
3
3
u
The overall hardness of this water is 384 mg/L as CaCO
3
.
Write the differential equation defining the efficiency of disinfection and
explain its components
This is the differential equation for disinfection:
N
k
N
kC
dt
dN
n
*
³
³
In this equation, N is the number (or activity) of the pathogens, k is the coefficient
of specific lethality, C is the concentration of the disinfectant, and n is an
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 Spring '10
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