In this video, I walk through the calculations needed to make two buffers: 1L of 0.15M phosphate buffer @ pH 7.4 and 250mL of 0.1M citrate buffer @ pH 6
I have to say that this is the most clearly presented and straightforward step by step I've seen in all of my searches for a protocol site that does exactly this!! Naturally you have to know some MATH (like algebra to solve for x and some log base 10 flips)! Most sites are just SO overly complicated so thank you VERY much for putting this up. Found it just when I needed it and it worked like a charm!!! THANK YOU THANK YOU THANK YOU!!!
hi, thankyou for ur great explanation! but, can i ask a question? how do we find recipe for phosphate-citrate buffer from stock solution: k2hpo4, citric acid, and distiilled water. because it’s a different stock, not only phosphate or not only citrate. and i’m confuse how to calculate it. thankyou!✨
I was just wondering, if I wanted to make a buffer for myself how would I arrive at what the concentration of that buffer should be? Ie how was 0.15 M and 0.1 M chosen? Was it just a random pick or are there rules that govern this choice
I have to say, the theory and practice are completely different. I followed the step and got the buffer, but pH is 6.93, far away from 7.4. Based on experience, If you want to get a pH 7.4 0.15M phosphate buffer, the ratio of 1M Na2HPO4 to 1M NaH2PO4 should be 4:1, then dilute to 0.15M. This video can only be used for homework.
You may be correct. There are other factors which contribute to pH that are not given by this theoretical problem. However, your pH value seems pretty far off from the theoretical pH. My guess is something else is amiss, like a mis-calibrated pH meter. In any case, I'd like to offer an easier way to make your buffer. Just add 0.15 M NaH2PO4 at a slightly lower volume than needed and adjust to pH 7.4 with NaOH..only have to weigh one salt and only final dilution to volume needed.
Hello! Comment from one who has looked into the practical use of this a bit now, and is thoroughly confused: For us lab people out there, it seems like using a different pKa for monobasic sodium phosphate is more accurate. monobasic sodium phosphate has, according to pubchem, a pKa of "6.8-7.2 (depending on the physicochemical characteristics during pKa determination)". Most tables that I find in lab procedures seem to use ca 6.8 as their pKa. (see for example one here www.sciencegateway.org/protocols/cellbio/appendix/phosb.htm ). Obviously, in this table, pKa cannot be 7.21, as the ratio of base and acid is far from 50/50 around pH 7.2. When you look at pH 6.8 however, the ratios are close to 50/50. And if we take the pH you got from your pH meter as an example @Saxit: If the real pKa was 6.8, then if you add the amounts given in the video, you should get a pH of 7, not 7.4. Now that is a lot closer to what you actually got. I am however still confused as to what is meant by "physiochemical charcteristics". Seems like these could be different from lab to lab?
There are 3 pKa's to chose from for citric acid. 6.4 is the one closes to the pH you want. Here is a reference for you: echa.europa.eu/registration-dossier/-/registered-dossier/14189/4/22
I have to say that this is the most clearly presented and straightforward step by step I've seen in all of my searches for a protocol site that does exactly this!! Naturally you have to know some MATH (like algebra to solve for x and some log base 10 flips)! Most sites are just SO overly complicated so thank you VERY much for putting this up. Found it just when I needed it and it worked like a charm!!! THANK YOU THANK YOU THANK YOU!!!
You are amazing. This is so clearly, thank you mate.
hi, thankyou for ur great explanation! but, can i ask a question? how do we find recipe for phosphate-citrate buffer from stock solution: k2hpo4, citric acid, and distiilled water. because it’s a different stock, not only phosphate or not only citrate. and i’m confuse how to calculate it. thankyou!✨
Are we going to mix them equally afterwards or by why ratio to get the calculated pH?
Nice job
I was just wondering, if I wanted to make a buffer for myself how would I arrive at what the concentration of that buffer should be? Ie how was 0.15 M and 0.1 M chosen? Was it just a random pick or are there rules that govern this choice
Well, it depends on what you want. For example, if it is a mobile phase, concentrations are usually 20 or 10 mmol.
Is it applicable for anhydrous precursor?
Letsss gooo💪🏿💪🏿💪🏿💪🏿
may i ask how did you come up with the ratio 1.55?
It's to cancel the Log10 on the other side of the equation. 10^7.4-7.21 = 1.55
Why at one end you using the concentration and on the other the moles
I have a question , how can u find out the ratio of base/ acid= 0.398 for citrate buffer?
You calculate 6 - 6.4 = -0.4. Then you antholagarithmic this value (10^-0.4) =0.398
How did u got 0.059 ?
pKa of disodium citrate is 5,4
It would really help if you wrote the actual equations that you are using
Henderson-Hasselbach equation
Not getting it😢
I have to say, the theory and practice are completely different. I followed the step and got the buffer, but pH is 6.93, far away from 7.4. Based on experience, If you want to get a pH 7.4 0.15M phosphate buffer, the ratio of 1M Na2HPO4 to 1M NaH2PO4 should be 4:1, then dilute to 0.15M. This video can only be used for homework.
You may be correct. There are other factors which contribute to pH that are not given by this theoretical problem. However, your pH value seems pretty far off from the theoretical pH. My guess is something else is amiss, like a mis-calibrated pH meter. In any case, I'd like to offer an easier way to make your buffer. Just add 0.15 M NaH2PO4 at a slightly lower volume than needed and adjust to pH 7.4 with NaOH..only have to weigh one salt and only final dilution to volume needed.
Hello! Comment from one who has looked into the practical use of this a bit now, and is thoroughly confused:
For us lab people out there, it seems like using a different pKa for monobasic sodium phosphate is more accurate.
monobasic sodium phosphate has, according to pubchem, a pKa of "6.8-7.2 (depending on the physicochemical characteristics during pKa determination)". Most tables that I find in lab procedures seem to use ca 6.8 as their pKa. (see for example one here www.sciencegateway.org/protocols/cellbio/appendix/phosb.htm ).
Obviously, in this table, pKa cannot be 7.21, as the ratio of base and acid is far from 50/50 around pH 7.2. When you look at pH 6.8 however, the ratios are close to 50/50.
And if we take the pH you got from your pH meter as an example @Saxit:
If the real pKa was 6.8, then if you add the amounts given in the video, you should get a pH of 7, not 7.4. Now that is a lot closer to what you actually got.
I am however still confused as to what is meant by "physiochemical charcteristics". Seems like these could be different from lab to lab?
pKa of disodium citrate is 5,4
There are 3 pKa's to chose from for citric acid. 6.4 is the one closes to the pH you want. Here is a reference for you: echa.europa.eu/registration-dossier/-/registered-dossier/14189/4/22