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Homework Help: Another buffer problem

  1. Sep 17, 2011 #1
    1. The problem statement, all variables and given/known data
    Prepare 500ml of a reaction buffer containing .82% MgCl2, 62.5 mM glucose, 950 ATP, and 100mM Tris -Cl, pH 7.8 Use the stock solutions you have prepared

    we had to prepare in previous problems:

    500ml 1.75M glucose
    25mL 2.5% glucose
    2L of 1.8 Tris, pH 8.5

    2. Relevant equations
    C1V1 = C2V2
    Pka Tris = 8.1
    glucose mol mass = 180.16
    ATP mol mass = 507.8


    3. The attempt at a solution

    my calculation for MgCl2:

    .82% = .82g/100ml = 8.2g/L
    15% = 15g/100ml = 150g/L


    150*x = 8.2*500

    x = 28mL stck 15% MgCl2

    My calculation for glucose

    1.75M glucose = 315g/L
    62.5mM = 11.2 g/L


    11.2*500 = 315*x

    x = 17.7 ml 1.75M glucose stock

    Here is my calculation for ATP

    5mM ATP = 3g/L
    950nM ATP = .00048g/L


    3*x = .00048*500

    x =.08ml of stocK 5mM ATP

    My calculation for the Tris I am not sure about, can I use my original pH 8.5 solution the prof asked me to prepare, or do I have to start over with the Tris acid and base components and use henderson H equation? does this all look right so far?
  2. jcsd
  3. Sep 17, 2011 #2


    User Avatar

    Staff: Mentor

    C1V1 = C2V2 works for molar concentrations as well, you don't have to convert them to g/L.

    My guess is you should prepare new buffer from HH equation.
  4. Sep 17, 2011 #3
    is the rest of it right?
  5. Sep 17, 2011 #4


    User Avatar

    Staff: Mentor

    Looks OK, but I just skimmed.
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