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Finding the pH of TSP

  1. Sep 28, 2006 #1
    We have 45.0g of Na3PO4 per liter. We know it is very basic but need the pH.
    I don't have the answers to all exercises, so if you could check my work, that'd be great.

    So, we have g, but moles would be more useful.
    So 45g x (1 mol/163.937) = 2.7 x 10^-1 mol.

    We know that strong bases completely dissociate in water.
    Therefore, [Na3PO4]=[OH-].
    So, since pOH = - log of all that = 0.569
    Therefore: pH = 14 - 0.569 = 13.431 which is indeed pretty basic.

    Any mistake somewhere?

    Thank you,

    Last edited: Sep 28, 2006
  2. jcsd
  3. Sep 28, 2006 #2


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  4. Sep 28, 2006 #3


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    You need to incorporate the equilibrium constant toward solving this problem.
  5. Sep 28, 2006 #4
    We do not have the equilibrium constant, and if they don't give us and don't tell us to refer to a table, it means we have to find a way around it (without an ICE table)...
  6. Sep 29, 2006 #5


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    No way. You will either use dissociation constant or it'll be pure guesswork.
  7. Sep 30, 2006 #6
    That's exactly why I assumed that, since they said that it was very basic, it completely dissociated in H2O, and it's why I went on with calculations without an ICE table.

    Well, I'll just assume it's right and see what the correction is when we get it.
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