Draw a titration curve without pH value?
I was titrating for my chemistry thesis, but forgot to measure the pH. The burette contained sodium hydroxide solution with a concentration of c=0.15 mol/l. In the Erlenmeyer flask below it, I had 10 ml of acetylsalicylic acid dissolved in ethanol (c=0.17 mol/l) and 3 drops of phenolphthalein as an indicator. It took 1.6 ml of sodium hydroxide solution for the indicator to change.
Can I draw a titration curve for this even though I haven't measured the pH? I would appreciate an answer, as I'm just around the corner. 🙂
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Hello Lasuppe
Unfortunately, the exact course of the titration can no longer be reconstructed. However, you can calculate the pH at the beginning, at the equivalence point and at the end of the titration and thus draw a curve.
Do you know how to calculate these things or do you need help?
Greetings, Fabio
Hello, I measured the pH before titration and it was 6.54, but how the pH is calculated at the end of titration, I don’t know. Could you please help me?
Sure! The pH at the end of the titration will approach the pH of 0.15M NaOH, which would be pH=13.18
You are titrating your solution with NaOH, whose concentration is 0.15M. This means that at the end the pH is 0.15M NaOH
The pH of strong bases is calculated with the following formula:
pH=14+log(c(A-)), where A- is the base.
So in your case: 14 + log(0.15) = 13.18
Thank you. Could you explain the route?
No.
How do you want to draw a curve if you don’t have data points?
You only have a measured value at 1.6 mL. More not.
But phenolphthalein gets pink when the pH is 8 to 9.8, can’t I do anything with it?
No.
You only have a measurement. You don’t know how it is before or after. You only have the knowledge that the envelope is 1.6 mL.
Take it as a lesson. Next time, you won’t forget the pH electrode.
Okay, thanks for the answer!
You don’t know the pK’s value of ASS. Then you cannot theoretically calculate the titration curve.
Looking at the pKs value would be the smallest problem.