# Re: mass imbalance problem

```
The mass-balance results look ok to me. I'm guessing that you are not
accounting for the stoichiometric coefficient of uranium in the species. In
the output, the molality applies to the molality of the species. You must
multiply by the stoichiometric coefficient of uranium in the species and
sum the results to obtain the total molality of uranium.

In the following example:

4.2e-4 = 5.078e-005*3 + 3.882e-005*3 + 3.467e-005*4 + 8.014e-006 +
3.630e-006 + 5.466e-007 + ...

David

U(6)            4.200e-004
(UO2)3(OH)7-     5.078e-005  4.854e-005    -4.294    -4.314    -0.020
(UO2)3(OH)5+     3.882e-005  3.711e-005    -4.411    -4.431    -0.020
(UO2)4(OH)7+     3.467e-005  3.314e-005    -4.460    -4.480    -0.020
UO2(OH)3-        8.014e-006  7.661e-006    -5.096    -5.116    -0.020
UO2(CO3)2-2      3.630e-006  3.030e-006    -5.440    -5.519    -0.078
UO2CO3           5.466e-007  5.468e-007    -6.262    -6.262     0.000
UO2OH+           2.174e-007  2.078e-007    -6.663    -6.682    -0.020
UO2(CO3)3-4      6.291e-008  3.055e-008    -7.201    -7.515    -0.314
(UO2)3(OH)4+2    3.270e-009  2.730e-009    -8.485    -8.564    -0.078
(UO2)2(OH)2+2    3.116e-009  2.601e-009    -8.506    -8.585    -0.078
UO2+2            6.496e-010  5.423e-010    -9.187    -9.266    -0.078
UO2SO4           9.341e-011  9.344e-011   -10.030   -10.029     0.000
UO2(OH)4-2       8.831e-012  7.372e-012   -11.054   -11.132    -0.078
UO2NO3+          9.089e-013  8.688e-013   -12.041   -12.061    -0.020
(UO2)3(CO3)6-6   1.413e-013  2.781e-014   -12.850   -13.556    -0.706
UO2(SO4)2-2      1.334e-013  1.114e-013   -12.875   -12.953    -0.078
(UO2)2OH+3       5.349e-014  3.563e-014   -13.272   -13.448    -0.176
UO2Cl+           4.302e-014  4.112e-014   -13.366   -13.386    -0.020
UO2Cl2           1.132e-019  1.132e-019   -18.946   -18.946     0.000

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

```

Complete Water Resources Division Software