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Homework Help: Formulas from question that BATE pH calculator gave me

  1. Oct 29, 2007 #1
    Hello, I am EXTREMELY glad I found this forum.

    I used a chemistry calculator that was posted by a poster here in a signature (BATE calculator from ChemBuddy) and it gave me an instant result to a problem I was trying to solve for a while, and that I should have been able to do on my own. I was given a problem that at one point in the solving of it I needed to find the pH of a solution. I knew the concentration of the HA ([HA]=0.200) and i had the information to find the first and second pKa (pKa1=2.34, pKa2=9.69) (the acid was Alinine, the amino acid). I needed to use this to find the pH of the solution at this point. From there I can find the rest of the problem, but it seemed to me that I couldn't get pH from that amount of information. The BATE calculator gave me a pH of 1.55, which seems like it COULD be right to me. I'm not sure. The big deal is knowing the way that the calculator could get that pH for me.

    EDIT:I just found the formulas. They are WAY too complicated for my tiny mind. And there is no way I was meant to find it like that, so it's back to square 1 for me.

    Also, in case I'm doing this all wrong, the question is as follows:

    I need to prepare 4.00 L of a 0.200 M Alanine buffer with a pH of 5.0. I have the following reagents available:
    • Alanine (solid) in its zwtterionic form (net charge of zero, pI=6.00) at molecular weight 89.0 g/mol.
    • 0.01M HCl
    • Water

    Find the amount of each reagent required.

    I know how much alanine is required (0.800 mol = 71.2g), and the amount of water is simple subtraction, but the volume of HCl solution is giving me trouble.
    Last edited: Oct 29, 2007
  2. jcsd
  3. Oct 30, 2007 #2
    I used the calculator again to get my final answers, but it was essentially trial and error. I won't get full marks for the question because I didn't use any normal design to find the answer, but the calculator has finally gotten me a solid answer.

    However, I could still use an explanation as to how to solve this question if it were to come up on a final exam. Any help you can give is still welcomed.

    EDIT: HOORAY! I just figured it out for myself. It turned out I actually had done it right the first time I tried, but I doubted myself and changed it. Thanks anyways, and the BATE calculator I was linked from this site is fantastic.
    Last edited: Oct 30, 2007
  4. Nov 1, 2007 #3


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    That is a problem! Don't come to depend on a calculator to find your answers without a complete understanding of the process unless you can use the calculator on your test!
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