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Thread: would someone help with biochem, I give up! (hints included)

  1. #1 would someone help with biochem, I give up! (hints included) 
    Forum Freshman
    Join Date
    Sep 2007
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    here is my data from lab:

    Buffer1: HPO4- weight 3.412g; original pH
    Buffer 2: HEPES wt: 1.090g original pH 10.08

    buffer1:
    pH of 0.1M: 7.5;
    pH of 0.01: 7.72;
    pH of 0.001M: 7.87

    buffer2:
    PH of 0.1M: 7.5
    ph of 0.01 M: 7.42
    pH of 0.001M: 7.42

    The problem will be done for one of the buffers made.

    A) What is the ratio of A-/HA in your buffer after you adjusted its pH to the required value? (pH goal: 7.5)

    B) How many micromoles of A- and HA are present in the solution?

    C) If you now add 3 mL of 1 M NaOH, will you still have a valid buffer?

    If necessary, here are the pka values and molecular weights: HEPES: pka 7.55; mw= 238.3; phosphate (HPO4-) pka1: 2.12 pka2: 7.21; pka 3: 12.32; mw=142.0

    HERE ARE HINTS I HAVE BEEN GIVEN:

    A. Use the Henderson Hasselbach equation.
    B. micromole = 0.001 mole
    you know that the HA + A- have to equal number of moles in the 0.1 M solution
    C. Will all of the HA form to the A- form be converted? Or will some of it remain?

    Thank you very much!!!


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  3. #2  
    Universal Mind John Galt's Avatar
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    Jul 2005
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    14,169
    Would you like to indicate any thoughts you have had on how to approach this problem. There may well be people here who can help you with it. There is probably no one who will do it for you.


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  4. #3  
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    I know I need to use the henderson hasselbalch equation to start with. How do I find the concentrations to plug them in?
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