Chemistry 3A

You want to make the following buffer: 5% glucose, 100 mM tris and 10 mM EDTA in a final voume of 300ml. Your stock solutions are 20% glucose, 1M tris and 0.5M EDTA. The diluent is distilled water. Determine how much of each you will add to make the desired buffer.

I know this so far::

1- Glucose
DF = C2 / C1 = 5% (DIVIDE) 20% = 0.25

V1 - DF X V2 = 0.25 X 300 ml = 75 ml

2 - Tris Stock = 1 M = 1000 mM

DF = C2 / C1 = 100 mM (DIVIDE) 1000 mM = 0.1

V1 - DF X V2 = 0.1 X 300 ml = 30 ml

Is this right so far?

asked by Katie
  1. Yes, both are right. Good work.

    posted by DrBob222
  2. I am doing the same problem.
    I got as far as you, including:

    DF = C2/C1 = 10 mM /500mM = 0.02 EDTA
    V1= DF x V2 = 0.02 x 300mL = 6 mL

    ...Now i am not sure what to do with this information. I would appreciate the help.

    posted by Eddie
  3. add up the three volumes:
    75mL + 30mL + 6 mL = 111mL
    The question tells us that the total final volume of the buffer is 300mL, so add enough water to your solute to bring it up to that desired volume:

    300mL - 111mL = 189mL

    So you would combine 111mL of the solutes to 189mL of the diluent, which is water, to get a final volume of 300mL.

    posted by QueenOf6

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