Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: tiramisucheese on April 17, 2015, 04:53:55 PM
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We just started buffers yesterday, and I feel like I got run over by a truck with this material. It takes time to settle, but tomorrow we have lab and we're supposed to design an experiment using this information that we just learned. I could use some guidance in how to approach setting up a buffer solution. Guidelines for this part of the experiment below:
Prepare 50 mL of solution buffered at pH 5.00. The buffer must be designed so the pH changes no more than 0.10 units with the addition of 0.001 moles of acid or base. Once the solution is prepared, you will test to determine if you were successful. You should also make a non-buffered solution at pH 5.00 and test it as well.
The following will be available for you to use to make the solutions. Be sure to choose the buffer pair best suited to the assigned conditions.
1.acetic acid/sodium acetate
2.formic acid/sodium formate
3.benzoic acid/sodium benzoate
HCl and sodium hydroxide solutions will also be available to test the resulting solutions and/or adjust pH.
Many thanks!
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You have two things to determine, the concentration needed based on the buffering capacity required -- no more than 0.1 pH units for 0.001 moles acid or base) and the pH target. You can determine the secon one with Henderson-Hasselbach. Did you learn that formula?
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Yes, I do know the Henderson-Hasselbalch equation! I think where I get lost is where that 0.1 pH units part comes in. How do I work that in?
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Do you know how to calculate new pH, after the addition of the strong acid or base?
http://www.chembuddy.com/?left=buffers&right=pH-change
Try to describe your buffer with a set of equations. One will be for the initial buffer, the other (actually not an equation but inequality) for the buffer after addition of the acid/base.