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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Orcio_Dojek on September 15, 2021, 08:20:17 AM

Title: NaOH + KCl buffer solution
Post by: Orcio_Dojek on September 15, 2021, 08:20:17 AM
I found this recipe:

http://delloyd.50megs.com/moreinfo/buffers2.html

12 mL 0,2 M NaOH + 50 mL 0,2 KCl = pH 12,00

Years ago it was advised by National Bureau of Standards in US.

Question is - NaOH absorbs CO2 from the air.

Does this solution need to be used as soon as made - OR - after some time (4 - 10 hours), because it NEEDS to absorb some amount of CO2 ?
Title: Re: NaOH + KCl buffer solution
Post by: Borek on September 15, 2021, 12:30:53 PM
Atmospheric CO2 absorption is way too unpredictable to be part of a reliable procedure.

But there is definitely something wrong here, I would expect pH of the solution to be around 12.4, not 12.0.
Title: Re: NaOH + KCl buffer solution
Post by: Babcock_Hall on September 17, 2021, 01:02:03 PM
The numbers at the link are consistent with p. 152 of Perrin and Dempsey's book "Buffers for pH and metal ion control", although the volumes at the link are all twice as large as those in the book.  The reference in the book is to Bates and Bower (1956).
Title: Re: NaOH + KCl buffer solution
Post by: Borek on September 17, 2021, 02:46:41 PM
The numbers at the link are consistent with p. 152 of Perrin and Dempsey's book "Buffers for pH and metal ion control", although the volumes at the link are all twice as large as those in the book.  The reference in the book is to Bates and Bower (1956).

Interesting. These are not very high ionic strength solutions (definitely beyond DH, but just around 0.2), so it is quite surprising that the difference between calculated pH and the one they report is so large.