Amount of base needed to titrate to pH 10.00

AI Thread Summary
To determine the minimum volume of 2.00 M NaOH needed to titrate a 50.0 mL sample of 1.00 M diprotic acid H2A to a pH of 10.00, one must consider both the complete neutralization of the acid and the additional base required to achieve the desired pH. The initial calculation indicates that 50.0 mL of NaOH is needed to neutralize the acid completely, but this volume does not account for the extra base required to raise the pH beyond neutral. The confusion arises from the distinction between neutralization and achieving a specific pH level, as not all acid is neutralized at pH 10. The discussion highlights the importance of understanding the relationship between pH and pKa in titration scenarios. Ultimately, the correct answer must reflect the additional volume of base necessary to reach the target pH.
Teemo
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Homework Statement


A 50.0 mL sample of a 1.00 M solution of a diprotic acid
H2A (Ka1 = 1.0 × 10–6
and Ka2 = 1.0 × 10–10) is titrated
with 2.00 M NaOH. What is the minimum volume of
2.00 M NaOH needed to reach a pH of 10.00?
(A) 12.5 mL
(B) 37.5 mL
(C) 25.0 mL
(D) 50.0 mL

Homework Equations


pH=-log[H+]

The Attempt at a Solution


I believe I am missing something extremely obvious. I find that NaOH, being a strong base will completely neutralize the acid and then additional base will be required to have the pH reach 10.00. So I found moles of hydrogen, being .05*1.00.*2. I then divided by molarity of the NaOH to find volume of NaOH required to completely neutralize it, and find 50.0 mL. Now this is where I get confused. D is the highest answer, and only has enough base to neutralize the acid, not to dissociate and to increase pH.
 
Physics news on Phys.org
Not all acid is neutralized at pH 10.0.

Do you know when pH=pKa?
 
Oh wow, sorry, I'm stupid. Thanks.
 
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