The pH range of a borate-phosphate buffer solution can be taken as the range of the phosphate and borate buffers separately?
Hey there Javier Ernesto Vilaso Cadre! You know, borate-phosphate buffer solutions are pretty fascinating. Now, I got the lowdown for you Javier Ernesto Vilaso Cadre. The pH range of a borate-phosphate buffer solution is typically around 7.0 to 8.6. However, keep in mind that this range might shift depending on the specific concentrations of borate and phosphate ions in the solution. Plese feel free to dive deeper into the world of buffers, my friend Javier Ernesto Vilaso Cadre.
Dear Javier Ernesto Vilaso Cadre
This case is pretty complicated and it depends on a lot of things beyond the concentrations of borate and phosphate.
One critical factor is how much base you have in the system. As you know, phosphoric acid by itself with the addition of base can take you all the way from pH ~1 (in fact, from pH12. So boric acid does NOT act as a base in this system. To form a buffer you'll need to add a true base, such as NaOH or KOH or ammonia.
About formation of one of these BPO4 hydrates see for example US 2375638, Englund (1945).
However, condensation of the two acids can occur at various molar ratios of B:P. US 3375138 (Mather, 1968) describes stable gels formed at molar B:P ratios of
1:2 - 1:7, and their usefulness in electrochemical cells. Naturally, these gels are very acidic and the main species conducting electricity there is H(+). Formation, composition and properties of these gels depend on preparation conditions. I'm not sure what happens when the B:P molar ratio is >1.
Returning to the base issue, how much base would you need to add to various boric-phosphoric mixtures to hydrolyze most of the B-O-P bonds and "force" a normal buffer behavior? I'm afraid this remains your special challenge, but isn't chemistry interesting?
Good luck!
Emanuel Cooper
borate-phosphate buffer solutions are versatile and can be applied in various research areas, including proteomics, biochemistry, and cell culture. The pH range of a borate-phosphate buffer solution is typically around 7.0 to 8.6
Thank you all for your interesting answers. However, my question comes from the fact that apparently mixed buffers such as phosphate-borate are intended to extend the pH range of a traditional buffer of a weak acid or base and its conjugate ion. For example, the Britton-Robinson buffer in its traditional formulation: acetic acid-phosphoric acid-boric acid allows buffer pH from 2 to 12. By changing the ratios of each acid and NaOH, the desired pH within that range can be achieved. But if for that Britton-Robinson buffer the pH range of 2 to 12 is known, what is the pH range for the buffer when there is no acetic acid/acetate in the system? I have seen phosphate-borate buffers for buffering pH 7, pH 8, pH 9, pH 10. So does that buffer really work in that range? Because for example borate buffers can only be used for pH 8 to 10. So the range of the phosphate-borate buffer is more limited than the borate buffer? Or does the range really extend from the phosphate range to the borate range if we take into account the separate pKa's? Unfortunately even in books this issue is confusing.
OK Javier Ernesto Vilaso Cadre
I misunderstood the scope of your question. I was referring to general buffer properties of boric-phosphoric mixtures at any - including high -concentrations and at practically any pH, while you were talking about Britton-Robinson-type buffers. For Britton - Robinson, the component concentrations are low (of the order of 30 mM for each component) so condensation of boric and phosphate together is not a major concern.
You will note that Britton-Robinson has an additional buffer for good coverage around pH 8, namely diethylbarbituric acid pKa ~7.8), because the combined buffer capacity of phosphate (pKa2 ~ 6.8) and boric acid (pKa ~9.0) at pH 8 is a bit low; but it should still be adequate for most purposes if you don't want to add diethylbarbituric acid.
Emanuel Cooper , thank you for your time to clarify my questions. So looking at it this way I can think that the pH range of a combined buffer like borate-phosphate will be taken by analyzing the pKa of each acid?
Hi Javier Ernesto Vilaso Cadre
Yes, the pKa's of the acids (and the conjugate acids of the bases) in the mixture are the most important factor. An additional important factor is the molarity of the buffer components. Other things being equal, buffer capacity is proportional to the concentration of the buffer.
Typically a 2-unit difference between pKa's in a buffer mixture is adequate for giving a good buffer capacity.
Best regards,
Emanuel Cooper
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