# How would I prepare a single phosphate buffered saline solution from three stock - (Feb/16/2008 )

How would I prepare a **single **__phosphate buffered saline solution that contains __**10 mM K2HPO4, 5 mM KH2PO4, and 0.85% (w/v) NaCl **from three stock solutions containing **1.0 M K2HPO4, 0.25M KH2PO4, and 8.5% (w/v) NaCl**. How many milliliters of each of the stock solutions and how many milliliters of deionized water would i need to prepare 500 mL of this phosphate buffered saline solution? I'm really confused and I need to prepare this for a lab __tomorrow__. Please please please help! Thanks in advance!

use:

Vi*Ci=Vf*Cf

hint- you have 2 concentrations (Ci and Cf) and a final volume (Vf) for each solution.

So would i take each solution and do that formula and then put them all together? like, if i did

Vi*Ci = Vf*Cf

where Vf is always 500 mL in all the equations, Cf is the final concentration for each solution, and Ci is the concentration for each stock solution... so

for the K2HPO4, i'd get Vi = 5 mL

for the KH2PO4, i'd get Vi = 10 mL

for the NaCl, i'd get Vi = 50 mL

would I just put all of those into the solution and bring the whole thing up to 500 mL with deinoized water?

Again, thanks so much!

Vi*Ci = Vf*Cf

where Vf is always 500 mL in all the equations, Cf is the final concentration for each solution, and Ci is the concentration for each stock solution... so

for the K2HPO4, i'd get Vi = 5 mL

for the KH2PO4, i'd get Vi = 10 mL

for the NaCl, i'd get Vi = 50 mL

would I just put all of those into the solution and bring the whole thing up to 500 mL with deinoized water?

Again, thanks so much!

That's right. You first add the reagent and then bring to volume. The calculations are right as well.

Thank you both so much!