I am having trouble understanding this question. I don\'t need every single valu
ID: 883061 • Letter: I
Question
I am having trouble understanding this question. I don't need every single value worked out I just want to understand what to do so I can work the rest out myself!
The question is written exactly as writtten:
The pK of an acid is 4.16. Calculate the pH of a solution of the acid if it is titrated to the following extents. Use the value associated with your student ID: extent of titration with NaOH, percent
0
1
2
3
4
5
6
7
8
9
28
71
33....
The istructions say,
Show all Calculations, give your pH value to two decimal places
My Student ID number is 1
I really just need help understanding the problem and how I should work it out, I don't want every single pH answer to the solution of the acid if it was titrated to all of the extents that are requested. I truly just want to learn and understand!
Thanks for your help and time!
Explanation / Answer
Given pKa = 4.16
we will use the equation,
pH = pKa + log[salt]/[acid]
when 0% titration is done, all we have is the acid so,
Ka = [H+][A-]/[HA]
let HA = 1 and x be the amount of acid disssociated then,
Ka = x^2/(HA-x), with x being a small amount, the equation reduces to,
Ka = x^2
pKa = -log[Ka]
Ka = 6.92 x 10^-5 = x^2
x = [H+] = 8.32 x 10^-3 M
pH = 2.08
When 5% titration is done,
5% acid has formed salt, 95% is remaining thus,
pH = 4.16 + log(5/95)
= 2.88
when 50% of titration is done, we would have half of acid reacted to form salt, so,
pH = 4.16 + log(50/50)
pH = 4.16
Similarly other values can be substituted in the equation to calculate the pH.
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