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Posted by on Sunday, June 5, 2011 at 8:33am.

You made up a saturated solution of calcium sulfate (CaSO4). The temp is 25 degrees Celsius. You then add 5.00*10^-3 of sodium sulfate (NaSO4). What are the concentrations of calcium and sulfate after equilibrium is reached? The pKs of CaSO4 is 4.58.

I know the Ks of CaSO4 to be 10^(-4.58) which equals 2.63E-5 but then what?

  • Chem - , Sunday, June 5, 2011 at 9:39pm

    CaSO4 ==> Ca^2+ + SO4^2-
    Ksp = (Ca^2+)(SO4^2-) = 2.63E-5
    From CaSO4 alone;
    (Ca^2+) = x
    (SO4^2-) = x

    Na2SO4 ==> 2Na^+ + SO4^2-
    You added 5.00E-3 WHAT? Is that molar? If so, then Na^2+ = 2*5.00E-3M
    and (SO4^2-) = 0.005M
    Plug all of this into Ksp for CaSO4.
    Ksp = (x)(x+0.005) = 2.63E-5
    Solve for x, then x + 0.005.

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