normal sodium phosphate buffer recipe is to mix a appropriate amount of salt (NA2HPO4) and weak acid (NAH2PO4). my question is if i take any of these chemicals and set pH to desired pH i.e. 7.4 would it work as a buffer?
Yes. By definition any solution that can resist pH changes is considered a buffer. Technically even water is a buffer, albeit a poor one. NaH2PO4 is a buffer, adding acids or bases does not change the fact it is a buffer. It's buffering range is ~5.8-8.0 so yes it is a buffer at 7.4. Technically, you may lose it's buffering capacity if you go higher than 8.0 or lower than 5.8, but keep in mind it is still a buffer solution, it just is outside it's buffering range.
in my opinion it could replace your buffer, when using NaH2PO4 together with NaOH.
the corresponding part of NaH2PO4 will "react" to Na2HPO4 + H2O, hence the composition will be as using di-Sodiumhydrogenphosphate and Sodiumdihydrogenphoasphate.
Mr. Babele, please tell my, whats wrong in my thought
Regards, Jochen
You can make a phosphate buffer using the weak acid, H2PO4, with addition of NaOH. The base will react and form HPO4 - the conjugate base of H2PO4. Therefore, with conjugate acid and base present, you will have a buffered system.
However, it's more ideal to simply use the Henderson–Hasselbalch equation to calculate how much of each (H2PO4, HPO4) you will need then do the slight adjustment of pH with NaOH.
Yes. By definition any solution that can resist pH changes is considered a buffer. Technically even water is a buffer, albeit a poor one. NaH2PO4 is a buffer, adding acids or bases does not change the fact it is a buffer. It's buffering range is ~5.8-8.0 so yes it is a buffer at 7.4. Technically, you may lose it's buffering capacity if you go higher than 8.0 or lower than 5.8, but keep in mind it is still a buffer solution, it just is outside it's buffering range.
The simplest answer is yes. If molarity is not important you can prepare your solution with either phosphate and then add acid or base to adjust the pH. The concentration of the acid or base is important cause you don't want to dilute your buffer solution too much. If molarity is critical then dissolve either phosphate without all the solvent (if your final solution volume is 250 mL, just use 230 mL for example) then add acid or base toadjust pH and finally make up to the mark.
Absolutely. The end result will be the same. But note that you can not start with Na2HPO4 and titrate down with acid because you will end up with a higher ionic strength. There will be too much sodium from the beginning and you will be introducing anions to titrate the pH down.
i am grateful to all for wonderful insights specially Daniel Lee Adams.
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