Zeba M.

asked • 11/17/16

How do I make a buffer with buffer capacity of 35.0 mM?

I have to make a buffer with a pH of 7. The solution's buffer capacity has to be 35.0 mM. Then I have to calculate how many mL of .1 M HCl will break my buffer. The professor will come around and break the buffer based on how many mL of HCl you tell her to use to break it.
I am going to use NaH2PO4 and Na2HPO4 to prepare a 100 mL of the buffer solution.
I do not understand how to make sure my buffer has 35.0 mM buffer capacity. I also do not understand how to calculate how many mL of HCl will break my buffer.
I don't know if you can help me with this question, but do you think my professor will be grading me based on the exact amount of mL of HCl that will break the buffer or would she just be looking to see if the buffer actually breaks? Thank you!
ps. I did make my buffer and it did end up having pH of 7 but it only took 7 mL of .1 M HCl to break which didn't seem right to me. I am wondering if the concentration of my buffer was to weak? [HA]=.0181 M and [A-]= .0035 M

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