Solution Calculations

Tris $($tris$[$hydroxymethyl$]$aminomethane$)$ is a commonly used buffer because it buffers over

normal biological range $(pH7$ to $9),$ it is non$-$toxic to cells and is relatively inexpensive. Tris is

supplied as a crystalline solid. Tris that is not conjugated to any other chemical is called "Tris

base." When Tris base is dissolved in water, the $pH$ will be more than $10$ and the $pH$ will need

to be lowered by titrating with a strong acid.

General Procedure to Bring a Solution to the Correct $pH$ Using a Strong Acid or Strong Base:

A$.$ Determine the amount of solute$($s$)$ required to get the correct concentration.

B$.$ Mix the solute$($s$)$ with part of the solvent required. Do not bring the solution to volume.

Start with $50\%$ to $75\%$ of the final volume desired.

C$.$ Place the solution on a magnetic stir plate, add a clean stir bar and stir. Place $pH$

electrodes of a calibrated $pH$ meter into the solution.

D$.$ Check the $pH.$

E$.$ Add a small amount of acid or base. Stir and check the pH$.$

F$.$ Repeat step $5$ until the $pH$ is correct

G$.$ Bring the solution to the proper volume. Recheck and record the $pH.$

$H.$ If you overshoot the $pH$ or overshoot the volume$-$BEGIN AGAIN.

I. When the $pH$ is adjusted correctly, pour the solution into a graduated cylinder and bring

to the correct volume with solvent.