8 You need 100mM Tris pH 8 for your project In your lab you

8. You need 100mM Tris, pH 8 for your project. In your lab you find a bottle of 1M Tris, pH 8 and decide to dilute it to the concentration you need (100mM). You decide 50mL will be more than enough. What volume of 1M Tris will you need to make the 50mL of 100mM Tris? Be certain to include units in your answer and show all of your work.

9. Now you need 25mM Tris in a volume of 250mL. What volume of your 100mM Tris will you need? Be certain to include units in your answer and show all of your work.

Solution

We need to prepare 100mM Tris, and then 25 mM Tris, pH 8.0. The stock solution is 1M i.e. 1000mM Tris.

To prepare 100mM Tris, we use the formula C₁V₁=C₂V₂,

where C₁=Initial concentration(mM) C₂=Final/Required concentration(mM)
   V₁=Initial Volume(mL) V₂=Final/Required volume(mL)

Now, to prepare 50ml 100mM Tris from the stock,

C₁V₁=C₂V₂

1000 X V₁ = 100 X 50
V₁ = (100 X 50)/1000
= 5000/1000
V₁ = 5 mL. Thus, we will require 5 mL of the stock 1M Tris pH 8.0 to prepare 100mM Tris pH 8.0.

Now, to prepare 25mM Tris from 100mM Tris,

C₁V₁=C₂V₂

100 X V₁ = 25 X 250
V₁ = (25 X 250)/100
   = 6250/100
V₁ = 62.5 mL. Thus, we will require 62.5 mL of the 100mM Tris pH 8.0 to prepare 250 mL of 25mM Tris pH 8.0.