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PH of Aqueous Solution

  1. Aug 2, 2009 #1
    [Solved] pH of Aqueous Solution

    1. The problem statement, all variables and given/known data
    Calculate the pH of the following aqueous solution prepared by adding 3.0L HBr(g), measured at 27 degrees Celsius, 757 mmHg pressure, to sufficient water to give 0.10L of solution.

    2. Relevant equations
    pH = -log[H+]

    3. The attempt at a solution
    I'm not sure how to handle a question with gas? Is there another equation I'm supposed to use? The answer says -0.08, which doesn't seem to make sense...

    I tried to do this question by first writing the equation
    HBr(g) + H20(l) --> Br- + H30+
    I found the number of moles of HBr gas to be 37.07...mol, and this is where my understanding fails me and I have no idea what to do. I even tried using n=cv which didn't work...

    Please help!
    Last edited: Aug 3, 2009
  2. jcsd
  3. Aug 2, 2009 #2
    It's possible to have negative pH. Just look at the formula for pH you have written.

    If you have 37.07 mol of HBr, dissolved in water, how much H+ do you have?
  4. Aug 3, 2009 #3


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    I'm not going to do the math for you but your answer for moles of HBr is waaaaay too high. Remember that under STP, an ideal gas has but one mole for every 23 L! You are only 2 degrees and 3 mm Hg away from that. Thus, a rough estimate of the number of moles is 3/23 or about 0.13 moles of HBr. In 0.1 liter that would be less than pH 0.1 but not much less.
  5. Aug 3, 2009 #4
    ok thanks, i think i got it....
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