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How to calculate Delta pH and Total Buffer Range

We were doing a lab in biology which included testing how basic and acidic different liquid substances were, andwe would add different amounts of drops of NCI and NaOH liquid to see how good of a buffer it was. I have the data but it wants me to find the  Delta pH and Total Buffer Range,  and I cannot find the instructions anywhere on how to do this. Here's what I have for Tap Water, I'll try my best to type one of them  out since I can't seem to find an option to send/paste photos on this. Thanks in advance for the help.


Tap Water
Zero drops
Acid at 9.25
Basic 7.0

5 drops
Acid 3.35
Basic 11.4
 
10 drops
Acid 7.2
Basic 11.63

15 drops
Acid 3.1
Base 11.11
 
20 drops
Acid 3.0
Base 11.85
 
25 drops
Acid 2.9
Base 11.95

How do I calculate the ΔpH and Total Buffer Range from this data?

Comments

I can't follow your data - are these pH values what the pH was after adding those amounts of acid and base?
 
In other words, after you added 10 drops of the HCl, your pH was 7.2, and a parallel sample after 10 drops of base the pH was 11.63?  I think that would also be a typo, if I am reading the rest of the data correctly...
 
Are all of these samples of the SAME substance, just with different amounts of HCl and NaOH added? 
 
Tap Water
Zero drops
Acid at 9.25
Basic 7.0
 
What does this mean?  What did you do with the tap water?  What does "Acid at 9.25" mean?  That pH is higher than 7, so that is not acidic.  "Basic 7.0" doesn't make any sense either - for a substance to be basic, the pH would be greater than 7.
Unless you can post a lot more detailed information about what you did, I don't know how to interpret any of this data.
 
I would be happy to work with you through this and figure it out, but we would need to go over the lab procedure and what substances were added to what. We would need to schedule a tutoring session to do that, in order to communicate back and forth and exchange the documents.

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