# Re: DO input concentration

```
It's a little confusing, but PHREEQC wants to know the number of moles of
oxygen in the zero valence state. To get that, you need to take the total
number of milligrams of oxygen and divide by 16.  It really does not matter
whether the total milligrams is specified to be O or O2; the number of
milligrams of O is equal to the number of milligrams of O2.

If you use "as O2", you will divide by 32, but this gives the number of
moles of O2, whereas PHREEQC wants the number of moles of just plain O.

David

David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled

"Bruno Haerens"
<bruno.haerens@xxxxxxxx        To:       <dlpark@xxxxxxxx>
uven.ac.be>                    cc:
Subject:  DO input concentration
10/28/2003 09:48 AM

David,

I'm a bit confused about the input concentration for DO in mg/l.
If I have 4mgO2/L, should I than enter 4mg/L for O(0)?
I tried to find out, and this gave me the correct result of 1.25e-5molO2/L
and 2.5e-5molO(0)/L
is this correct?

This is maybe a stupid question, but I got confused why not entering conc
"as O2", but then I get 6.284e-005molO2/l as a result, which is 2mgO2/l.

best regards,
bruno

------------------------------------
Reading input data for simulation 1.
------------------------------------

DATABASE C:\Program Files\Phreeqc\Phreeqc.dat
SOLUTION 1
temp      25
pH        7.92
pe        4
redox     pe
units     mg/l
density   1
O(0)      4.02
Na        19.8
K         4.9
Ca        73.3
Mg        33.5
Cl        78
S(6)      95 as SO4
N(5)      55 as NO3
Alkalinity 140
water    1 # kg
-------------------------------------------
Beginning of initial solution calculations.
-------------------------------------------

Initial solution 1.

-----------------------------Solution
composition------------------------------

Elements           Molality       Moles

Alkalinity       2.799e-003  2.799e-003
Ca               1.830e-003  1.830e-003
Cl               2.201e-003  2.201e-003
K                1.254e-004  1.254e-004
Mg               1.379e-003  1.379e-003
N(5)             8.874e-004  8.874e-004
Na               8.617e-004  8.617e-004
O(0)             2.514e-004  2.514e-004
S(6)             9.894e-004  9.894e-004

----------------------------Description of
solution----------------------------

pH  =   7.920
pe  =   4.000
Activity of water  =   1.000
Ionic strength  =  1.079e-002
Mass of water (kg)  =  1.000e+000
Total carbon (mol/kg)  =  2.823e-003
Total CO2 (mol/kg)  =  2.823e-003
Temperature (deg C)  =  25.000
Electrical balance (eq)  = -4.625e-004
Percent error, 100*(Cat-|An|)/(Cat+|An|)  =  -3.26
Iterations  =   7
Total H  = 1.110152e+002
Total O  = 5.552149e+001

---------------------------------Redox
couples---------------------------------

Redox couple             pe  Eh (volts)

O(-2)/O(0)          12.6251      0.7469

----------------------------Distribution of
species----------------------------

Log       Log
Log
Species            Molality    Activity  Molality  Activity
Gamma

OH-              9.282e-007  8.325e-007    -6.032    -6.080
-0.047
H+               1.320e-008  1.202e-008    -7.880    -7.920
-0.040
H2O              5.551e+001  9.998e-001     1.744    -0.000
0.000
C(4)            2.823e-003
HCO3-            2.656e-003  2.396e-003    -2.576    -2.621
-0.045
CO2              6.462e-005  6.478e-005    -4.190    -4.189
0.001
CaHCO3+          3.731e-005  3.367e-005    -4.428    -4.473
-0.045
MgHCO3+          2.590e-005  2.329e-005    -4.587    -4.633
-0.046
CaCO3            1.725e-005  1.729e-005    -4.763    -4.762
0.001
CO3-2            1.410e-005  9.346e-006    -4.851    -5.029
-0.179
MgCO3            7.389e-006  7.407e-006    -5.131    -5.130
0.001
NaHCO3           1.038e-006  1.041e-006    -5.984    -5.983
0.001
NaCO3-           1.496e-007  1.344e-007    -6.825    -6.871
-0.046
Ca              1.830e-003
Ca+2             1.663e-003  1.101e-003    -2.779    -2.958
-0.179
CaSO4            1.120e-004  1.123e-004    -3.951    -3.950
0.001
CaHCO3+          3.731e-005  3.367e-005    -4.428    -4.473
-0.045
CaCO3            1.725e-005  1.729e-005    -4.763    -4.762
0.001
CaOH+            1.691e-008  1.520e-008    -7.772    -7.818
-0.046
Cl              2.201e-003
Cl-              2.201e-003  1.975e-003    -2.657    -2.704
-0.047
H(0)            2.042e-027
H2               1.021e-027  1.023e-027   -26.991   -26.990
0.001
K               1.254e-004
K+               1.249e-004  1.121e-004    -3.903    -3.950
-0.047
KSO4-            4.510e-007  4.054e-007    -6.346    -6.392
-0.046
KOH              3.224e-011  3.232e-011   -10.492   -10.491
0.001
Mg              1.379e-003
Mg+2             1.246e-003  8.306e-004    -2.905    -3.081
-0.176
MgSO4            9.923e-005  9.948e-005    -4.003    -4.002
0.001
MgHCO3+          2.590e-005  2.329e-005    -4.587    -4.633
-0.046
MgCO3            7.389e-006  7.407e-006    -5.131    -5.130
0.001
MgOH+            2.790e-007  2.508e-007    -6.554    -6.601
-0.046
N(5)            8.874e-004
NO3-             8.874e-004  7.946e-004    -3.052    -3.100
-0.048
Na              8.617e-004
Na+              8.583e-004  7.725e-004    -3.066    -3.112
-0.046
NaSO4-           2.201e-006  1.978e-006    -5.657    -5.704
-0.046
NaHCO3           1.038e-006  1.041e-006    -5.984    -5.983
0.001
NaCO3-           1.496e-007  1.344e-007    -6.825    -6.871
-0.046
NaOH             4.234e-010  4.244e-010    -9.373    -9.372
0.001
O(0)            2.514e-004
O2               1.257e-004  1.260e-004    -3.901    -3.900
0.001
S(6)            9.894e-004
SO4-2            7.755e-004  5.109e-004    -3.110    -3.292
-0.181
CaSO4            1.120e-004  1.123e-004    -3.951    -3.950
0.001
MgSO4            9.923e-005  9.948e-005    -4.003    -4.002
0.001
NaSO4-           2.201e-006  1.978e-006    -5.657    -5.704
-0.046
KSO4-            4.510e-007  4.054e-007    -6.346    -6.392
-0.046
HSO4-            6.644e-010  5.972e-010    -9.178    -9.224
-0.046

```

Complete Water Resources Division Software