I have phosphate buffer that is pH 6.9-7.2 that I bring to pH 8.5 with hydroxide. The problem is that overnight the solutions saturate with CO2 and the pH drops to around 6.5 (the pKa of carbonic acid). I was considering using another buffer component, such as carbonate to hold the higher pH, thinking that added CO2 will now be less able to reduce the pH....any suggestions, experience or comments on this? The chemistry can't be altered too much, so I can't use exotic buffer components such as tris.
2006-09-08 05:34:28 · 5 answers · asked by Robert L. D 2 in Science & Mathematics ➔ Chemistry
There is no peroxide in this system. I am aware of how to buy buffers and have exhausted commercial sources because they don't meet my specific needs - I am worried about specific chemical interactions and require there to only be phosphate around but may be able to take carbonate as well. Who buys buffers, anyways?
2006-09-08 05:45:36 · update #1
Buffer solution should be able to maintan pH at a fairly constant level with the addition of small amt of acid or base. addition of hydroxide-OH- would make your buffer more alkaline. The OH- will react with conjugate acid (salt) to form a base(same as in your phosphate buffer)and giving pH8.5. You have already upset the buffer system by addition of OH-.
2006-09-09 21:41:41 · answer #1 · answered by alien 1 · 0⤊ 1⤋
umm....I would just make a new buffer. I have never heard of a buffer dropping pH that much with just atmospheric CO2. I am pretty sure the conversion of CO2 to carbonic acid is not that fast. I think there is something else wrong with the buffer, and you should just make a new one.
I suppose you can add carbonate to raise the pH, but that is a lot to go using a weak base like carbonate, so you might be also really throwing off the concentrations of your components. Not to mention you would be adding a lot of the carbonate's counter cation as well, which can significantly affect your chemistry.
I would really just make a new buffer.
2006-09-08 12:29:26 · answer #2 · answered by tsubame_z 2 · 0⤊ 0⤋
I've never heard of this before... Is your buffer too dilute? It is too weird for a buffer to change its pH so much overnight just because of atmospheric CO2... Doesn't sound like a real buffer !?!
Are you sure your reagents are OK?
Do you also leave the bottle of the buffer open?
2006-09-08 06:07:06 · answer #3 · answered by bellerophon 6 · 0⤊ 0⤋
You are messing up your buffer system by changing its content. Buy a buffer for your needed pH and there should be no problem.
2006-09-08 05:38:51 · answer #4 · answered by PetLover 3 · 0⤊ 1⤋
Peroxide loses stability fast, can you use something else?
2006-09-08 05:41:15 · answer #5 · answered by Fleur de Lis 7 · 0⤊ 1⤋