Titrating H2SO4 with two bases

[woodS]

I am trying to titrate an acid with two bases (0.001m Na2CO3 and 0.001m Na3PO4)but my code is not giving me what I am looking for. Any suggestion would be appreciated.
Thank you

Code: [Select]

USER_PUNCH
-head Spec_Cond
PUNCH SC
SELECTED_OUTPUT
    -file                 titration.out.xls
    -ph                   true
    -ionic_strength       true
    -charge_balance       true
    -activities           H+  Na+

SOLUTION 1
    temp      25
    pH        7 charge
    pe        4
    redox     pe
    units     mol/l
    density   1
    S(6)      0.05
    -water    0.1 # kg

PHASES
Thenardite
    Na2SO4 = 2Na+ + SO4-2
    log_k     0.7
    delta_h   1.12 kcal
Thermonatrite
    Na2CO3:H2O = CO3-2 + H2O + 2Na+
    log_k     0.125
    delta_h   -2.802 kcal

EQUILIBRIUM_PHASES 1
    CO2(g)    -3.5 10
    Thenardite 0 0
    Thermonatrite 0 0

REACTION 1
    Thermonatrite 1
    Na3PO4     1
    0.002 moles in 150 steps

USER_GRAPH 1
-headings Addition "SO4-2" "Na+" "pH"
-axis_titles "Added Na2CO3 and Na3PO4 (mol)","molality per Kg" ,"pH"
-chart_title  "Titration Curve"
     -axis_scale x_axis 0 auto
     -axis_scale y_axis 1e-2 auto auto auto
     -axis_scale sy_axis 1 14 1
-start
10 pH=-LA("H+")
20 GRAPH_X RXN
30 GRAPH_Y MOL("SO4-2"), MOL("Na+")
40 GRAPH_SY pH
-end
-active                 true

END



[John Mahoney]

instead of 0.002 moles try

REACTION 1
    Thermonatrite 1
    Na3PO4     1
    0.02 moles in 150 steps

You just need to add more base.  You should get a good titration curve then.  Rereading your post,  I think you should actually be using 0.01 moles,  your initial text said 0.001 moles of each.   So go back and check the output file to see what you are really adding.   It reaches a steady pH after only a few steps. 

[woodS]

Thank you!