Preparation of phosphate buffers?
1. 0.2M Phosphate (pH 7.0) Buffer
2. 0.02 M Phosphate (pH 7.5) Buffer
3. 0.2 M Phospahte (pH 6.6) Buffer
i have potassium dihydrogen phosphate & disodium hydrogen phosphate but i can also get NaOH and HCl...i have a method to prepare 0.025 M phosphate buffer where i use 3.40g KH2PO4 & 3.55g Na2HPO4 but the pH of this solution is not stated...i need the actual lab procedure.and i need it for the 3 buffer solutions above.and the pH to go with it....i dont know what to do..nor what equations to use
Answer:
If this is a homework problem you can do it by the book. If you actually need these buffers to be accurate then you need to go to the library, get a book on biochemical methods, and look up how to prepare the buffers. Because the theory doesn't quite give the right answer. I had to do this once for some consulting that I did, and I've got the reference in my office. Check back here in 12 hours.
Don't use any equations. Simply use potassium dihydrogen phosphate and adjust with NaOH.
The only true buffer is 0.025M quantities of KH2PO4 & Na2HPO4 which gives pH of 6.88 @ 20ºC. The other pHs aren't in the true buffer region but can be made by either adding phosphoric acid to lower or sodium hydroxide to raise the pH using a previously calibrated pH meter.
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