Saturday, May 9, 2009

How To Make a Tris Buffer

Tris is a chemical with basic properties, having a pKa of 8.1. It can be used to buffer solutions from drastic pH changes, keeping them in the pH range of 7.0 to 9.0.

Make any Tris-HCl buffer in this pH range, at any molarity using these simple steps

1. Calculate Moles of Tris Base

Determine the number of moles of Tris base needed by multiplying the desired molar concentration of buffer by the volume of buffer being made.

mol/L * L = moles needed

2. Calculate Mass of Tris Base

Determine the mass of Tris base to weigh by multiplying the number of moles by the molecular weight (121.14 g/mol) of Tris.

moles needed * g/mol = g

3. Dissolve Tris Base in Water

Dissolve the required mass of Tris into a volume of deionized water approximately 1/3 of the desired volume of buffer to be made.

4. Adjust the pH

Using a pH meter, titrate the solution of Tris with 1M hydrochloric acid (HCl) until the correct pH is reached.

5. Bring to Volume

Add the TrisHCl mixture to a volumetric flask of the desired volume and add deionized water as required to complete the solution.

What You Need:

* Standard labware: beakers, flasks, graduated cylinders, stirbars etc.
* pH meter and probe.
* Stirring hotplate.
* Tris base powder and hydrochloric acid (HCl).


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