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Homework Help: Molar Solubility Questions

  1. Aug 6, 2013 #1
    1. The problem statement, all variables and given/known data
    I have worked these two problems to the best of my knowledge and I keep getting the wrong answer (I'm not sure what the right answer is). Here are the questions:

    1. At a certain temperature the solubility of barium chromate (BaCrO4) is 1.9×10-5 mol/L. What is the Ksp of BaCrO4 at this temperature?
    2. What is the molar solubility of silver phosphate (Ag3PO4) in water? Ksp = 1.8×10-18.

    2. Relevant equations

    The relevant equations are Ksp=([products]/[reactants])

    3. The attempt at a solution
    For question 1: BaCrO4⇔Ba2+ + CrO42-
    Ksp=[Ba2+][CrO42-]/1 (since it is a solid)
    Ksp=[1.9x10-5]2=3.61x10-10 = 3.6x10-10

    For question 2: Ag3PO4⇔3Ag+ + PO43-
    1.8x10-18 = ([Ag+]3[PO43-])/1
    1.8x10-18 = [3x]3[x]
    1.8x10-18 = [27x4] then divide both sides by 27
    6.6666667x10-20 = x4 then do the fourth root on both sides
    x = 1.6068568x10-5 = 1.6x10-5

    I would very much appreciate any insight into this. Thank you!
  2. jcsd
  3. Aug 6, 2013 #2
    Your approach looks fine to me unless you have done some calculation mistake.

    What are the correct answers?
  4. Aug 6, 2013 #3
    It is an online homework, like a quiz, that we are allowed multiple attempts on. It doesn't give me the correct answer. I'll email the prof. Thanks!
  5. Jan 4, 2017 #4
    where is this coming from??? [27x4]
  6. Jan 5, 2017 #5


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    Staff: Mentor

    Which part of [itex](3x)^3x = 27x^4[/itex] is unclear to you? This is a pretty basic algebra.
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