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Posted by on Sunday, May 19, 2013 at 9:33pm.

A certain weak base has a Kb of 7.80 × 10-7. What concentration of this base will produce a pH of 10.17?

  • chemistry - , Sunday, May 19, 2013 at 10:11pm

    pH = 10.17.
    pOH = 14-10.17 = 3.83
    pOH = -log(OH^-)
    3.83 = etc.
    OH^- = about 1.4E-4 but that's an estimate.
    ...........BH + H2O ==> BH2^+ + OH^-
    I..........x............0........0
    C.........-y............y........y
    E.........x-y...........y.........y

    Kb = 7.8E-7 = (BH2^+)(OH^-)/(BH)
    You know OH^- = estimated 1.4E-4
    You know BH2^+ = OH^- = y
    Solve for x. You don't have two unknowns; only x is unknown.

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