Calculations involving acids and bases

Click For Summary

Discussion Overview

The discussion revolves around calculating the volumes of two solutions, sodium acetate (NaOAc) and acetic acid (HOAc), based on the final pH of a mixed solution. Participants explore the necessary equations and constants needed to solve the problem, including the acid dissociation constant (Ka) and the Henderson-Hasselbalch equation.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant seeks to determine the volumes of NaOAc and HOAc given a final pH of 4 and a total volume of 20 ml.
  • Another participant emphasizes the need for the Ka of acetic acid to proceed with the calculations, suggesting that it is essential to look up its numerical value.
  • A participant mentions finding the pKa of acetic acid as 4.8, which leads to the calculation of Ka as 1.58*10^-5.
  • There is a request for feedback on the participant's work, indicating uncertainty about the appropriate equations to use.
  • One participant notes that the topic is elementary and commonly covered in various resources, suggesting that self-resolution may be beneficial.
  • Another participant suggests looking up the Henderson-Hasselbalch equation, indicating its relevance to the problem at hand.

Areas of Agreement / Disagreement

Participants generally agree on the necessity of the Ka value and the relevance of the Henderson-Hasselbalch equation, but there is no consensus on the specific steps to solve the problem or the correctness of the calculations presented.

Contextual Notes

Participants express uncertainty about the next steps in the calculations and the appropriate equations to apply, indicating potential limitations in their understanding of the underlying theory.

sergey_le
Messages
77
Reaction score
15
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.]
 
Last edited by a moderator:
Physics news on Phys.org
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).
 

Similar threads

Chemistry Moles of NaOH to Create Buffer Solution pH=6 in 0.42M Ethanoic Acid
  • · Replies 3 ·
Replies
3
Views
3K
Chemistry How to take into account autoprotolysis in weak base solution?
  • · Replies 8 ·
Replies
8
Views
2K
Chemistry How to calculate pH at equivalence point using this alternative?
  • · Replies 7 ·
Replies
7
Views
2K
Chemistry Comparing methods of computing pH at equivalence point in titration
  • · Replies 4 ·
Replies
4
Views
2K
Titration of acetic acid w/ NaOH problem
  • · Replies 2 ·
Replies
2
Views
3K
Chemistry Understanding how to calculate pH of a buffer solution
  • · Replies 2 ·
Replies
2
Views
2K
Chemistry Help with Complex Acid-Base Titration
  • · Replies 1 ·
Replies
1
Views
2K
Number of HCl Equivalents in 100mL of pH 4 Solution
  • · Replies 8 ·
Replies
8
Views
2K
Calculate the pH of a 0.20 M solution of iodic acid (HIO3).
  • · Replies 5 ·
Replies
5
Views
8K
Titration of amino acid with strong base
  • · Replies 16 ·
Replies
16
Views
4K