How to prepare your own pH buffers for pH meter calibration from scratch
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- čas přidán 7. 08. 2024
- This video shows you how to prepare pH 4 and pH 7 buffers for pH meter calibration using readily available low cost raw salts. These buffers have a strength of 0.1M. These are the amounts needed to prepare 250mL of buffer solution:
pH 4
Potassium Citrate 2.63g
Citric acid monohydrate 3.45g
(if using anhydrous citric acid, use 3.15g)
pH 7
Potassium Citrate 7.14g
Citric acid monohydrate 0.35g
(if using anhydrous citric acid, use 0.32g)
(Please notice that the Amazon links below are affiliate referral links. This means that if you click on them I may receive a commission from purchases. There is no additional cost to you, but it helps me to keep posting content for free.)
Class A Volumetric Flask (250mL)
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Beaker set
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Scale
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Citric Acid Monohydrate
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Citric Acid (anhydrous)
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Potassium Citrate
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Silicon ice cube trays (similar, but not exact ones shown in video)
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Impeccable style, full of accuracy, and very thorough! A great way to remind oneself, "don't be a savage!"
Thank you for all the amazing information you are providing.
My pleasure! Thanks for commenting!
Excellent info!
thanks colombian friend this is fire!
New subscriber, extremely helpful, thaaaanks man, thanks for taking the time
Thanks for the sub!
useful videos and tutorials. thank you very much for sharing your knowledge. ❤️ from philippines
My pleasure!
Hi His i love your videos, i wonder if u have time to make a video on chelating agents in hydroponics
I do always share your useful and interesting videos, I'm mot a savage LOL tank you very much for yours teachings
You are welcome! Thank you very much for sharing. Feel free to make topic suggestions for future videos.
So I just came across your channel and I am super glad I did. Looking at your list of videos I'm sure I'll be binge watching and attempting to play chemist and save some cash on all the commercial buffer solutions.
On this video I would have liked to see you test a commercial solution and your solution as proof of concept. Not that I don't trust you and all but I'm big on validation.
One thing I didn't see in your videos was the KCl "storage solution" that is always recommended for storing our ph probes. I mean Im no chemist but Im guessing there is more to it than just buying some potassium chloride solution and dropping my probe in. Just a thought.
Thanks for commenting and for watching the videos! I do hope you enjoy them!
About validation, sadly at the time I didn't have buffers to compare with. But that's certainly a good idea for a future video. My other video on preparing these solutions without a scale uses a pH meter to validate, so that is the method I would recommend to be more certain. If you have some calibration solutions available for the preparation of your new solutions.
About the storage solution, it is really as simple as it sounds. Buy potassium chloride and prepare a solution with 225g/L in distilled water and you can use that for electrode storage.
Thank you for the video! I'd like to add, when trying to weigh hundredths of a gram and you think its not adding any mass, try tapping the container and let the scale settle. It'll tell you where you're at and avoid over shooting sometimes. Hope that helps.
Thanks for your comment and suggestion! I'll give that a try next time.
Very good material. I appreciate your efforts. I have an important clue. At 7:21 when you transfer quantitatively from a beaker to a volumetric flask - you should use a small glass or plastic funnel. By pouring directly from the beaker to flask, you risk spilling beyond that narrow neck of the flask. Even the loss of one drop makes a difference. You then lose some of the substance, and the acid-base balance will not be maintained. Therefore, the pH will not be as assumed by the calculations, and precise weighing.
Thanks for your comment and suggestion! Precise transfers are in fact quite important in this case.
I totally appreciate how you simplified the diy by using potassium citrate and citric acid for both buffers. I wonder if you ever have any issues with the pH 7 buffer though? Couldn't help remembering that in general chemistry it's recommended to use citrate buffers ~ pH 3-6.3 or 6.2 because the third pKa is well below 7. So, in theory at least, it has almost no buffering capacity above that pKa. Then again, if you're freezing it immediately maybe it doesn't really need to do much buffering - just achieving the target pH 7 for a couple days from freeze-to-thaw in controlled environment, right? Very interested to know your thoughts... thank you!
Thanks for commenting. An acid will provide buffering capacity around +/-1 units away from its pKa. If you prepare a citric acid buffer at a pH of 7 it is true that its buffering capacity towards the upside will be much weaker than towards the downside (around only 30-40%), however it is still well enough what is necessary for electrode calibration. Bear in mind that the most important thing to buffer against in this case is changes from varying atmospheric CO2 levels, since CO2 generates an acid in water, this means that it is most critical to have good capacity towards the downside.
This is really useful always wanted to know how to make my own pH buffers. Would like to know the theory of pH buffers and how it's calculated also what is the stable shelf life of the solution? I'm curious why does the ready made commercial pH buffers expire? Does the solid chemicals salts such has potassium citrate and Citric acid monohydrate expire, can I keep these powered chemicals viable for a long time such as 10+ years to keep on making pH buffers? Thanks.
Buffers can expire because of microbial activity or because of reactions with atmospheric CO2, which alter buffer chemistry as a function of time. The buffers in this video would last for a long time frozen, but would spoil in a matter of days in the liquid state (since they contain no preservatives). In my other video, where I discuss preparing them without a scale, you can prepare much more stable buffers since this method allows you to use a preservative to keep microbial activity from damaging them.
@@ScienceinHydroponics Thank You for you reply.
@@ScienceinHydroponics I just made pH 4 and 7 buffers. It seems like my pH meter (Vivosun 4 in 1) requires pH buffers of 4, 6.86 and 9.18.
What is the correct dry ratio of potassium citrate and citric acid anhydrous for a pH buffer of 6.86 and pH buffer 9.18?
Thank you.
Hi Daniel, Is it possible to add Sodium Benzoate to this mix or will it alter the pH of the formula? Thank you again for sharing your knowledge.
You cannot add sodium benzoate to this mix since working without a calibrated meter means that precise additions are required and the benzoate would alter the buffer's pH. To add a preservative, see my video about how to prepare pH buffers without a scale, these ones do include a preservative.
@@ScienceinHydroponics Thank you! Daniel.
@@ScienceinHydroponics Thank You!
I think that there is a small mistake in the description (potassium citrate quantity for ph4 buffer solution: 2.36 gr instead of 2.63 gr). Thanks for the interesting content as always. There will be a similar video to make EC calibration solution?
Thanks for commenting! Yes, you were right, this has been fixed now. Also, yes, there will be a similar video for EC calibration solutions coming soon.
Hello David, Always a pleasure to follow your thorough content.
Is there a major difference between pH UP and pH DOWN solutions to this pH buffer solution?
If so, may I make a video request to enlighten us on the differences and how to mix your own pH UP and pH DOWN solutions?
Thanks for commenting! There is a big difference between these buffers and pH up/down solutions. I will make video about those in the future per your suggestion.
@@ScienceinHydroponics that's great to hear, Big thanks! I'm excited 😄
His name is Daniel
Yes I am also interested as well.
@@alexaguillon7904 lol He clearly said Daniel Fernandez, only god can explain why he comprehended "David" lol
Hey David I am new here
Very informative video
Can i replace potassium citrate by sodium citrate.
And how much sodium citrate should be needed to make a solution of ph 4 and 7
You could use sodium citrate, but you will need to recalculate the weights with the ratio of the molar mass between sodium and potassium citrates.
Thank you Sir. please share calculations
Thanks, I might to a video about them if more people ask!
How can prepare solutions pH=2 et pH=10 for étalonnage pH metre
very good video! But i have a question. There are different potassium citrate out there.. Some contain 35%, some 36% potassium. Does this make any difference? Thanks!
Try getting USP grade, which are higher purity. The higher the purity the more accurate the results will be.
Hey Dr. Is there anyway to stabilize the final solution? For long term storage. can you teach us how to use phosphorous acid to buffer and some raise the pH.
I have another video on pH buffers were I add preservatives, which you might find useful.
Hello David, new subscriber here. I find it hard to get potassium citrate , what can I substitute it with??
You could use sodium citrate as well.
Are there any preservatives that can be added to the solutions instead of freeing them?
Yes, but adding the preservatives modifies the pH, which means you cannot follow this process and add a preservative to get an adequate buffer. Please watch my other videos on buffer preparation to see how to prepare buffers including preservatives.
Hi
Please do the calculations and tell us how you understand the amounts??
Is it Henderson equation or what??
Thanks BTW.
Thanks for writing. These is not based on any single equation but on solving the equation system derived from mass balance, charge balance and all the chemical equilibrium reactions present in the solution. This is the best way to calculate pH for complex systems. The Henderson-Hasselbalch equation is a simplification that is really only accurate for monoprotic weak acids.
Awesome video. I can't find potassium citrate anywhere near me, I live in South Africa I've tried looking online but nothing. Is there another name for it in the food industry?
Try some lab suppliers. These guys seem to carry it in south africa chemlabsupplies.co.za/product/tri-potassium-citrate-
@@ScienceinHydroponics Thanks for the reply, you are great ty:D
Now how to prepare electrode storage solution?
Thanks for commenting! To prepare an electrode storage solution for a pH meter, dissolve 225g/L of Potassium Chloride in distilled water.
Wont the ph of distilled water matter in this?
No. Distilled water has almost no buffering capacity, so its pH is of no consequence.
I need recepie for ph 10 pleass
Thanks for writing. For a pH ten buffer you can use glycine and sodium hydroxide. I would suggest you buy a small amount of pH 10 buffer to calibrate your meter then follow the method on my other buffer solution video to prepare your pH 10 buffer using glycine and NaOH.
What if moisture inside of refrigerator add more water into these ice cubes? Would it affect the accuracy too much?
Not much, the buffer is able to resist things that attempt to change its pH. Since the buffering capacity of this added water is negligible, the effect on the pH will be very small.
@@ScienceinHydroponics Thanks for the great video and explanation. How these calculations were done?
They were done using chemical equibrium equations. You create a system of equations that represents the full aqueous system, then solve for the variables that interest you. The equations include all relevant chemical equilibria (all weak acid dissociations, water self-dissociation, etc), charge balance and mass balance. The systems are not super easy to solve, so I generally use Maxima or Mathematica for that.
@@ScienceinHydroponics Thank you! I don't think I am able to do these calculations :)
@9:55 Didn't you have exactly 3.45g before you then added more xD
Thanks for your comment! I know 🤦♂️