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Mass and Charge Balances

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    Systematic Treatment of Equilibrium:

    Step 1: Write the pertinent reactions

    Step 2: Write the charge balance equation

    Step 3: Write the mass balance equation.  There may be more than one

    Step 4: Write the equilibrium constant expression for each chemical reaction

    -This step is the only one in which activity coefficients appear

    Step 5: Count the equations and unknowns

    There should be as many equations as unknowns (chemical species).  If not, you must either find more equilibria or fix some concentrations at known values.

    Step 6: Solve for all unknowns




    1)  Write a charge balance expression for a solution containing Na+, Mg2+, Ca2+, H+, Cl-, H2CO3, HCO3-, CO32-, OH-, H2O










    2) What is mass balance? The quantity of all species in a solution containing a particular atom or group of atoms must equal the amount delivered to the solution. (Essentially a statement of the law of conservation of matter).

    Write out the mass balance equation for a solution of 0.25M H2CO3










    3) Write the pertinent reactions for a solution saturated with CaF2. NOTE: HF is a WEAK ACID and F- is a weak base.  Write the equilibrium constant expression for each of your equations.

    Kb = 1.49 x 10-11

    Ksp = 3.2 x 10-11










    4) Write the mass balance equation for the following equation:

    \[\ce{Ag2CO3_{(s)} ↔ 2Ag+ + CO3^2-}\nonumber\]













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