Question

Sometimes a reagent has more than one ingredient at very different concentrations. For example, here are the ingredients and their concentrations for TAE gel electrophoresis buffer:

40 mM tris

20 mM acetic acid

1 mM EDTA

TAE is often used in rather large volumes, and instead of making a large volume of dilute TAE, we make a relatively small volume (usually 1L at a time) of TAE that is 50 times more concentrated than the “working concentration.” We call this primary stock 50X (“fifty ex”) TAE. 50X TAE is made using

242g Tris base

57.1mL glacial acetic acid

100mL of 500mM EDTA (pH 8.0)

In a final volume of 1 L in aqueous (water) solution.

How much 50X TAE do you need to make 1L of 1X TAE? How much water do you need?

How much 50X TAE do you need to make 500 mL of 1X TAE? How much water do you need?

How much 50X TAE do you need to make 200 mL of 1X TAE? How much water do you need?

please show work :/

Answer 1

C1 * V1 = C2 * V2

(stock) (working solution)

Where C is the concentration

V is the volume

50X TAE to make 1L of 1X TAE

50 * V1 = 1 * 1

V1 = 0.02 L

Volume of 50X TAE needed = 0.02 L or 20mL

Volume of water needed = 1-0.02 = 0.98 L or 980 mL

50X TAE to make 500mL of 1X TAE

50 * V1 = 1 * 500

V1 = 10mL

Volume of 50X TAE needed = 50 mL

Volume of water needed = 500-50 = 450 mL

50X TAE to make 200mL of 1X TAE

50 * V1 = 1 * 200

V1 = 4mL

Volume of 50X TAE needed = 4mL

Volume of water needed = 200-4 = 196 mL