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Homework Help: How to calculate the pH

  1. Feb 28, 2010 #1

    Blazzok

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    1. The problem statement, all variables and given/known data
    I need to know how to do the following. If I have 1L of water with a pH of 7 and I add 1mL Vinegar with a pH of 2.4, what will the pH of the solution then be?
    I now need to get the pH of the solution back to 7 by adding ammonia which has a pH of 11.6. How much of that do I need to add?


    I dont need a solution to the problem, i just need to know the equations so that i can solve this problem.
     
    Blazzok, Feb 28, 2010
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  3. Feb 28, 2010 #2

    CompuChip

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    What is the definition of pH?
     
    CompuChip, Feb 28, 2010
  4. Feb 28, 2010 #3

    Blazzok

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    pH = please Help?? -.-
     
    Blazzok, Feb 28, 2010
  5. Feb 28, 2010 #4

    CompuChip

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    Hehe, that's not a definition, it's a corollary :P

    The pH of a solution is defined as -log [H+], minus the base-10 log of the concentration of H-ions. The trick is now to work with the concentrations. How many moles per litre do you have in both substances? How many when you put it together? Then how much is there in a litre of the new mixture?
     
    CompuChip, Feb 28, 2010
  6. Feb 28, 2010 #5

    Borek

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    Staff: Mentor

    Just don't forget vinegar and ammonia both mean weak acid/base, so just using concentration won't work.
     
    Borek, Feb 28, 2010
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