error in PMT question?
As part of an investigation, a student needed to prepare a buffer solution with a pH
value of 8.71. From the Ka value of phenol, the student thought that a mixture of phenol
and sodium phenoxide could be used to prepare this buffer solution.
The student decided to use a 0.200 mol dm–3 solution of phenol, mixed with an equal
volume of sodium phenoxide.
Use your knowledge of buffer solutions to determine the concentration of sodium
phenoxide solution that the student would need to mix with the 0.200 mol dm–3 phenol
solution.
This is the whole question and I am seeing people get 0.013. However when looking at the markscheme I'm doing the same equation and getting a huge number. This is because I don't have the Ka value. Is the Ka value supposed to be there or is it part of a different section of the question where you have to work it out?
value of 8.71. From the Ka value of phenol, the student thought that a mixture of phenol
and sodium phenoxide could be used to prepare this buffer solution.
The student decided to use a 0.200 mol dm–3 solution of phenol, mixed with an equal
volume of sodium phenoxide.
Use your knowledge of buffer solutions to determine the concentration of sodium
phenoxide solution that the student would need to mix with the 0.200 mol dm–3 phenol
solution.
This is the whole question and I am seeing people get 0.013. However when looking at the markscheme I'm doing the same equation and getting a huge number. This is because I don't have the Ka value. Is the Ka value supposed to be there or is it part of a different section of the question where you have to work it out?
Original post by Alesha_sk
As part of an investigation, a student needed to prepare a buffer solution with a pH
value of 8.71. From the Ka value of phenol, the student thought that a mixture of phenol
and sodium phenoxide could be used to prepare this buffer solution.
The student decided to use a 0.200 mol dm–3 solution of phenol, mixed with an equal
volume of sodium phenoxide.
Use your knowledge of buffer solutions to determine the concentration of sodium
phenoxide solution that the student would need to mix with the 0.200 mol dm–3 phenol
solution.
This is the whole question and I am seeing people get 0.013. However when looking at the markscheme I'm doing the same equation and getting a huge number. This is because I don't have the Ka value. Is the Ka value supposed to be there or is it part of a different section of the question where you have to work it out?
value of 8.71. From the Ka value of phenol, the student thought that a mixture of phenol
and sodium phenoxide could be used to prepare this buffer solution.
The student decided to use a 0.200 mol dm–3 solution of phenol, mixed with an equal
volume of sodium phenoxide.
Use your knowledge of buffer solutions to determine the concentration of sodium
phenoxide solution that the student would need to mix with the 0.200 mol dm–3 phenol
solution.
This is the whole question and I am seeing people get 0.013. However when looking at the markscheme I'm doing the same equation and getting a huge number. This is because I don't have the Ka value. Is the Ka value supposed to be there or is it part of a different section of the question where you have to work it out?
Hello Alesha_sk!
The Ka value of phenol is essential for solving this problem, as it is necessary to calculate the pH of the buffer solution. The Ka value may either be provided elsewhere in the investigation (perhaps earlier in the question) or expected to be known. If it is not given explicitly, you should use a known value from a reference source. The Ka of phenol is approximately 1.3 x 10^-10 (check out this value online), which represents the equilibrium constant for phenol’s dissociation into phenoxide ions and protons.
EDIT: Try to solve the problem, and if you encounter difficulty, let me know so I can provide additional tips to help you complete it.
Bye,
(edited 2 months ago)
Original post by Alesha_sk
As part of an investigation, a student needed to prepare a buffer solution with a pH
value of 8.71. From the Ka value of phenol, the student thought that a mixture of phenol
and sodium phenoxide could be used to prepare this buffer solution.
The student decided to use a 0.200 mol dm–3 solution of phenol, mixed with an equal
volume of sodium phenoxide.
Use your knowledge of buffer solutions to determine the concentration of sodium
phenoxide solution that the student would need to mix with the 0.200 mol dm–3 phenol
solution.
This is the whole question and I am seeing people get 0.013. However when looking at the markscheme I'm doing the same equation and getting a huge number. This is because I don't have the Ka value. Is the Ka value supposed to be there or is it part of a different section of the question where you have to work it out?
value of 8.71. From the Ka value of phenol, the student thought that a mixture of phenol
and sodium phenoxide could be used to prepare this buffer solution.
The student decided to use a 0.200 mol dm–3 solution of phenol, mixed with an equal
volume of sodium phenoxide.
Use your knowledge of buffer solutions to determine the concentration of sodium
phenoxide solution that the student would need to mix with the 0.200 mol dm–3 phenol
solution.
This is the whole question and I am seeing people get 0.013. However when looking at the markscheme I'm doing the same equation and getting a huge number. This is because I don't have the Ka value. Is the Ka value supposed to be there or is it part of a different section of the question where you have to work it out?
Yeah, they should have given you the pKa or Ka of phenol or got you to work it put previously (unless it was an undergraduate level question- then they could get you to give an estimate of it).
Do you happen to have a link to the sheet in question?
For now, if it is in fact not given, take the pKa of phenol to be 10, which is what an undergrad would typically estimate its pKa to be.
Original post by TypicalNerd
Yeah, they should have given you the pKa or Ka of phenol or got you to work it put previously (unless it was an undergraduate level question- then they could get you to give an estimate of it).
Do you happen to have a link to the sheet in question?
For now, if it is in fact not given, take the pKa of phenol to be 10, which is what an undergrad would typically estimate its pKa to be.
Do you happen to have a link to the sheet in question?
For now, if it is in fact not given, take the pKa of phenol to be 10, which is what an undergrad would typically estimate its pKa to be.
I couldn't find the link to the sheet, even though you asked Alesha directly.
Look at here: Previous Thread , this text is the same as the original post. Phenol Ka was mentioned in the previous thread.
I agree with everything else you wrote.
Bye,
(edited 2 months ago)
Original post by Nitrotoluene
I couldn't find the link to the sheet, even though you asked Alesha directly.
Look at here: Previous Thread , this text is the same as the original post. Phenol Ka was mentioned in the previous thread.
I agree with everything else you wrote.
Bye,
Sandro
Look at here: Previous Thread , this text is the same as the original post. Phenol Ka was mentioned in the previous thread.
I agree with everything else you wrote.
Bye,
It’s somewhere on physics and maths tutor (I can’t be bothered to look lol), but thanks for finding the question elsewhere and confirming that they should have included the Ka of phenol.
Interestingly the Ka value given in the question seems to be rounded up from the most highest value measured in water at 25°C that I am aware of (The Ka ranges from 1.00 x 10^-10 - 1.25 x 10^-10, corresponding to pKa values ranging from 9.9 to 10), though most sources I have come across suggest that it’s closer to 1.0 x 10^-10.
(edited 2 months ago)
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