If you hate doing mole calculations by hand, check out this PHREEQC tip. Good thing about the free software by USGS is that you can input the variables as mg/L (or other units) and it will first speciate the solutions to give you the molality and moles for each component.
Lets just use one example I have been working for last couple of days. I was trying to calculate amount of Ca+ required in the groundwater to result the amount of Na+2 measured in the sample. If we assume 100% ion exchange, then the calculation becomes simple. All you need is to figure out the mole ratio of Na+ and Ca+.
For this particular example, I actually did not use PHREEQC at all other than just getting my mole numbers. Well, I noticed that we have large charge balance error. Means I don’t have every component of the solution. Search my guide for Charge Balance Error to understand how PHREEQC could be used to determine the quality of a sample.
Enjoy. If you don’t want PHREEQC, use my free spreadsheet to calculate mole ratios.
==========================Input Code===================
TITLE Example
SOLUTION 1
units ppm
Ca 1
Mg .26
Na 506
K .9
Alkalinity 380.64 as HCO3
END
===========================================================
Note: You can add all of your cations and anions here. Once you are done, hit “RUN”
==========================Out Put===========================
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Reading data base.
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SOLUTION_MASTER_SPECIES
SOLUTION_SPECIES
PHASES
EXCHANGE_MASTER_SPECIES
EXCHANGE_SPECIES
SURFACE_MASTER_SPECIES
SURFACE_SPECIES
RATES
END
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Reading input data for simulation 1.
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DATABASE C:\Program Files\USGS\Phreeqc Interactive 2.15.0\phreeqc.dat
TITLE Example
SOLUTION 1
units ppm
Ca 1
Mg .26
Na 506
K .9
Alkalinity 380.64 as HCO3
END
—–
TITLE
—–
10 East (Underground) Sampled on 5/13/10
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Beginning of initial solution calculations.
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Initial solution 1.
—————————–Solution composition——————————
Elements Molality Moles
Alkalinity 6.244e-003 6.244e-003
Ca 2.497e-005 2.497e-005
K 2.304e-005 2.304e-005
Mg 1.070e-005 1.070e-005
Na 2.203e-002 2.203e-002
—————————-Description of solution—————————-
pH = 7.000
pe = 4.000
Activity of water = 0.999
Ionic strength = 1.416e-002
Mass of water (kg) = 1.000e+000
Total carbon (mol/kg) = 7.471e-003
Total CO2 (mol/kg) = 7.471e-003
Temperature (deg C) = 25.000
Electrical balance (eq) = 1.588e-002
Percent error, 100*(Cat-|An|)/(Cat+|An|) = 56.23
Iterations = 9
Total H = 1.110187e+002
Total O = 5.552740e+001
—————————-Distribution of species—————————-
Log Log Log
Species Molality Activity Molality Activity Gamma
OH- 1.131e-007 1.001e-007 -6.946 -7.000 -0.053
H+ 1.109e-007 1.000e-007 -6.955 -7.000 -0.045
H2O 5.551e+001 9.995e-001 1.744 -0.000 0.000
C(4) 7.471e-003
HCO3- 6.171e-003 5.500e-003 -2.210 -2.260 -0.050
CO2 1.233e-003 1.237e-003 -2.909 -2.908 0.001
NaHCO3 6.017e-005 6.036e-005 -4.221 -4.219 0.001
CO3-2 4.089e-006 2.579e-006 -5.388 -5.589 -0.200
CaHCO3+ 1.178e-006 1.049e-006 -5.929 -5.979 -0.050
NaCO3- 1.057e-006 9.374e-007 -5.976 -6.028 -0.052
MgHCO3+ 4.711e-007 4.180e-007 -6.327 -6.379 -0.052
CaCO3 6.459e-008 6.480e-008 -7.190 -7.188 0.001
MgCO3 1.593e-008 1.599e-008 -7.798 -7.796 0.001
Ca 2.497e-005
Ca+2 2.373e-005 1.496e-005 -4.625 -4.825 -0.200
CaHCO3+ 1.178e-006 1.049e-006 -5.929 -5.979 -0.050
CaCO3 6.459e-008 6.480e-008 -7.190 -7.188 0.001
CaOH+ 2.796e-011 2.481e-011 -10.553 -10.605 -0.052
H(0) 1.411e-025
H2 7.056e-026 7.079e-026 -25.151 -25.150 0.001
K 2.304e-005
K+ 2.304e-005 2.039e-005 -4.638 -4.691 -0.053
KOH 7.042e-013 7.065e-013 -12.152 -12.151 0.001
Mg 1.070e-005
Mg+2 1.022e-005 6.495e-006 -4.991 -5.187 -0.197
MgHCO3+ 4.711e-007 4.180e-007 -6.327 -6.379 -0.052
MgCO3 1.593e-008 1.599e-008 -7.798 -7.796 0.001
MgOH+ 2.657e-010 2.357e-010 -9.576 -9.628 -0.052
Na 2.203e-002
Na+ 2.197e-002 1.952e-002 -1.658 -1.710 -0.051
NaHCO3 6.017e-005 6.036e-005 -4.221 -4.219 0.001
NaCO3- 1.057e-006 9.374e-007 -5.976 -6.028 -0.052
NaOH 1.285e-009 1.289e-009 -8.891 -8.890 0.001
O(0) 0.000e+000
O2 0.000e+000 0.000e+000 -42.082 -42.080 0.001
——————————Saturation indices——————————-
Phase SI log IAP log KT
Aragonite -2.08 -10.41 -8.34 CaCO3
Calcite -1.93 -10.41 -8.48 CaCO3
CO2(g) -1.44 -2.91 -1.47 CO2
Dolomite -4.10 -21.19 -17.09 CaMg(CO3)2
H2(g) -22.00 -25.15 -3.15 H2
H2O(g) -1.51 -0.00 1.51 H2O
O2(g) -39.19 -42.08 -2.89 O2
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End of simulation.
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Reading input data for simulation 2.
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End of run.
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