4 May, 13:03

# You want to make the following buffer: 5% glucose, 100 mM tris and 10 mM EDTA in a final volume of 300ml. Your stock solutions are 20% glucose, IM tris and 0.5M EDTA. The solvent is distilled water. In the space provided determine how much of each you will add to make the desired buffer.

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1. 4 May, 14:52
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You'll need to add 75mL of glucose 20%, 30mL of tris 1M, 6mL of EDTA 0.5M and enough water to make up 300 mL.

Explanation:

To prepare the buffer we need to clearly determine the desired final concentrations of each regeant and the final volume, and then we'll see how to reach those concentrations starting from the available (stock) solutions.

Stock solutions:

20% glucose 1M tris (=1000mM) 0.5M EDTA (=500mM)

Final buffer:

5% glucose 100 mM tris 10 mM EDTA Water up to 300 mL

To calculate how much of each reagent we need to add to make the buffer we can use the formula C1*V1 = C2*V2, where C1 = concentration of stock solution, V1 = volume needed from the stock solution, C2 = desired concentration of the reagent in the buffer, V2 = volume of buffer we wish to prepare.

*Note that the units of volume/concentration must match, if the initial concentration is in M and the desired concentration is mM, we need to convert either the initial concentration to mM or the final concentration to M.

Glucose

C1*V1 = C2*V2

20% * V1 = 5% * 300 mL

V1 = 5% * 300 mL / 20%

V1 glucose = 75 mL

Tris

C1*V1 = C2*V2

1000mM * V1 = 100 mM * 300 mL

V1 = 100mM * 300mL / 1000 mM

V1 tris = 30mL

EDTA

C1*V1 = C2*V2

500mM * V1 = 10 mM * 300 mL

V1 = 10mM * 300mL / 500 mM

V1 EDTA = 6 mL

Final answer: you'll need to add 75mL of glucose 20%, 30mL of tris 1M, 6mL of EDTA and enough water to make up 300 mL.