Calculations involving acids and bases

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SUMMARY

The discussion centers on calculating the volumes of 0.1M sodium acetate (NaOAc) and 0.1M acetic acid (HOAc) solutions needed to achieve a final pH of 4 in a total volume of 20ml. The user correctly determined the hydrogen ion concentration as 1 x 10^-4 M and identified the need for the acid dissociation constant (Ka) of acetic acid, which is 1.58 x 10^-5 based on a pKa of 4.8. The Henderson-Hasselbalch equation is essential for solving this problem, as it relates pH, pKa, and the ratio of the concentrations of the acid and its conjugate base.

PREREQUISITES
  • Understanding of pH and hydrogen ion concentration calculations
  • Knowledge of acid dissociation constants (Ka and pKa)
  • Familiarity with the Henderson-Hasselbalch equation
  • Basic skills in algebra for rearranging equations
NEXT STEPS
  • Learn how to apply the Henderson-Hasselbalch equation in buffer solution calculations
  • Research the significance of Ka and pKa in acid-base chemistry
  • Practice problems involving calculations of pH in buffer solutions
  • Explore the relationship between concentration and volume in solution preparation
USEFUL FOR

Chemistry students, educators, and professionals involved in laboratory work or any field requiring acid-base calculations will benefit from this discussion.

sergey_le
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Summary:: finding ml of two solutions by the final pH

i have a NaOAc 0.1M and HOAc 0.1M , together the volume of the solutions is 20ml and the pH is 4. I need to find the volume of each solution.
I've tried to solve it for hours with no successes. i found the H+ concentration (-log(h)=4 ), it is 1*10^-4 M so in a 20 ml solution we got 2*10 ^-6 mol but I don't know what to do next. find the ka?

[Moderator's note: Moved from a technical forum and thus no template.]
 
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yes, you need the Ka, the acid dissociation constant of acetic acid. You have to look its numerical value up, there is no way to work it out. You may more likely find quoted not Ka but pKa, and you have to know what that means. Also look up 'Henderson Hasselbalch equation'.
 
Last edited:
epenguin said:
yes, you need the Ka, the acid dissociation constant of acetic acid. You have to look its numerical value up, there is no way to work it out. You may more likely find quoted not Ka but pKa, and you have to know what that means. Also look up 'Henderson Hasselbalch equation'.
i found the pka=4.8 so the ka is 1.58*10^-5.
i guess the big issue i have is understanding what equation i should use. i attached what idid so far ,can you give it a look and tell me where i am wrong?
 

Attachments

I was unable to open your attachment. However please realize this is very elementary theory covered in thousands of books or sites (and the most frequent subject of problems in this forum section) though if you can work it out yourself that is still better.
 
Google Henderson-Hasselbalch equation (although it is just a rearranged Ka definition).
 

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