Buffers for bluffers


No, not that kind…

A little while ago now I wrote a post entitled Amazing Alkaline Lemons?. It’s been very popular, sort of. Well, it’s elicited an awful lot of comments anyway. Quite a few have mentioned buffers, which are jolly important things. They also seem to be somewhat misunderstood. So here we go, buffers 101:

Buffers regulate pH (remember that pH is the scale that measures how acidic, or basic, a solution is), and they’re essential in the body. Without them, your blood pH would fluctuate, and that that would be a very bad thing indeed. Outside a very narrow pH range (7.38 to 7.42, which is essentially neutral) proteins are denatured and enzymes stop working. In short, your body would quickly stop functioning in a really quite fatal way.

So what is a buffer? A buffer is actually a mixture, of a weak acid and its salt. Or, as chemists would say, its ‘conjugate base‘. (I’m deliberately avoiding the word ‘alkali’, because alkali has a specific meaning and it would be wrong to use it in this situation – I mention this because the word ‘alkalising’ has come up more than once).

The main buffer system in the blood is the bicarbonate buffering system. We need it because our blood has to transport carbon dioxide out of our bodies, and when carbon dioxide is dissolved in solution it forms an acid called carbonic acid. If this weren’t somehow controlled, our blood pH would quickly plummet and, as I’ve already mentioned, we’d die. This would obviously be something of an evolutionary dead-end.

Chemistry to the rescue! Carbonic acid (H2CO3) forms, but it also breaks apart again to form hydrogen ions (H+) and bicarbonate ions (HCO3) producing something chemists call an equilibrium (symbolised by the funny two-way arrow you can see below).

H2CO3 ⇌ H+ + HCO3

Equilibria have a way of balancing themselves out, and this is key to how buffers work. If you add some extra hydrogen ions to a buffer system the equilibrium shifts to absorb those hydrogen ions, keeping the pH constant. Likewise, if an alkali (or base) is added, it goes the other way and actually causes more hydrogen ions to be released. This is remarkably difficult to budge, unless you swamp it with a really strong acid (or base).

As a result, your blood pH stays perfectly balanced, and a good thing too. And all you need for it to work is to breathe. I recommend that if you want to stay healthy you don’t stop doing that.

There are other important buffer systems in the body. One that gets mentioned quite a lot is the phosphate buffer system. This plays a relatively minor role in controlling blood pH, but it is pretty important for your cells. This buffer is made up of dihydrogen phosphate ions and hydrogen phosphate ions. Phosphate plays an important role in bone health, not to mention your body’s ability to use energy effectively. Fortunately, unless you have some kind of fairly serious health problem your kidneys do a cracking job of controlling phosphate levels, so there’s no need to worry too much about it, beyond aiming, as we all should, for a generally healthy diet.

So there we are. Buffers are a mixture, they form naturally in the body, you don’t really need to do anything to help them along, and they quietly keep you alive. Pretty cool bit of everyday chemistry really.

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15 thoughts on “Buffers for bluffers

  1. Pingback: Amazing alkaline lemons? | the chronicle flask

  2. Pingback: What’s in the water? | the chronicle flask

  3. Brilliant. What’s your opinion on Diatomaceous Earth ? Is it safe for human consumption ? Why would you consume it ?


  4. I enjoyed the “Amazing alkaline lemons?” post – I am writing here since the other thread is closed. I found this after stubbornly putting down my sisters claim that lemons would neutralize stomach acid.

    Being a chemist myself, I obviously saw no logic in that statement, but she would not believe me.
    But my conclusion was based on the assumption that the citric acid (triprotic) in natural lemons was fully protonated. But then I got to thinking: what if the pH of lemon juice is only equivalent to the di-protonated citric acid? In that case, the statement would essentially be correct, although that buffersystem would not allow for a pH of much above 3,1 (the pKa of fully protonated citric acid).

    A simple calculation with knowledge of the average citric acid content of lemons, and the pH of average lemon juice would reveal the protonation of the original citric acid, and whether the statement might be slightly correct after all. Anyway, I thought this would be an interesting observation 🙂

    – Nils


    • Hi, it’s an interesting thought. I can’t think why the lemon juice in citric acid wouldn’t be fully protonated, but anyway weak(er) acids can behave as proton acceptors in the presence of strong(er) acids (e.g. in the nitration mixture for the nitration of benzene). BUT that doesn’t mean they act to neutralise the acid. The number of dissociated H+ ions in the system should remain more or less constant. The trouble with calculations is that you don’t know the concentration of citric acid in a lemon. It seems to me that experiment is the way forward. Do you have access to a pH probe? (I don’t I’m afraid.) If so, all you need to do is put about 50 ml 1M hydrochloric acid in a beaker (stomach fluid averages between about 20-100 ml, so that should be a sensible amount), pop the pH probe in and then add drops of fresh lemon juice and observe whether the pH changes beyond the normal probe fluctuations. Let me know if you try it!


      • I am just a layperson, but I have been looking for an answer for some time now and as of yet have not found anything definitive. That is how I got here in the first place. From what I have read you seem to know what you are talking about. I am trying to find the best method of probiotic survival. Again, from what I have read, If you take them on an empty stomach, the stomach PH is too low for survival. If you take after a meal they will not survive the stomach acid. Supposedly research shows that if you take them with some fat, they survive best. So what would be ideal to take on an empty stomach with the probiotics to raise the PH in the stomach just enough, but less likely to kick in a lot of stomach acid?

        I would so appreciate getting some guidance on this.

        Thank you.


      • Hm, well, I am definitely not an expert on pro- or prebiotics – that’s a whole field of study in itself. I have heard the same thing though, that relatively little of the bacteria which are consumed are likely to make it to where they’re needed. It’s not just stomach acid, but other unfavourable conditions elsewhere in the digestive tract – bacterial destruction seems to be inevitable if you just swallow them in the regular way (several groups have been investigating fecal transplants though, nice). Bear in mind that our digestive systems evolved over millions of years to basically kill most bacteria we eat, on the basis that it’s more likely to be bad than good. However, I did find an article about microencapsulation of probiotics which you might find interesting. Of course the other thing is to try and include lots of prebiotic foods in your diet, anything with lots of fibre – onions, garlic, bananas and asparagus seem to get a lot of mentions – which will help you to maintain healthy gut flora.


  5. Thank you for your interesting information. Speaking from a layman’s point of view, I disbelieve lemon juice neutralises acid because when I eat it, I get heartburn! My best cure for burning indigestion is milk, although I’ve heard some people say that milk worsens their problem. :-)Sharon


    • Ah yes, I’ve been told that milk mainly ‘works’ because it’s cold (usually out of the fridge) and you’d get the same soothing effect with chilled water. Milk is a source of protein and sugars, and that would stimulate digestive juices, so it seems to me (I have no source for this mind you) that could well be counter-productive. Perhaps try ice water next time and see? 🙂


  6. In this and the ‘lemon’ article you claim that a pH of 7 is neutral, but this only applies at 25 deg. C or 298 K. The water-equilibrium or self-ionization of water is temperature-dependent. At an average body-temperature of 37 deg. C or 310 K, a pH of 6.80-6.81 is neutral. This does make blood slightly basic, relatively speaking.


    • You’re right. Although the ionic product of water is based on pure water, which blood isn’t, so I’m not sure how much of a difference that would make (carbon dioxide solubility being another factor). I’m also not sure, now I think about it, whether blood pH is traditionally measured fresh out of the body (at 37 degrees) or once it’s had some time to cool down. But even all that aside, the difference is only about 0.6 – less than 1 point on the pH scale – and while that is moving in the basic direction on the scale, it’s still safe to say that blood is effectively neutral.


      • I partly agree. Couldn’t find information about test-procedures when I first commented because I also wondered about this. But it looks like the pH is measured at laboratory-temperature.
        Most (or all) biology and biochemistry books I’ve read do state that blood is slightly alkaline. And I’m always a bit careful with logarithmic scales. When given a choice, I’d rather be in a 6.8 than a 7.4 earthquake.

        The best statement I’ve read lately about the food and blood pH is: [quote] The bottom line is that if you’re breathing and going about your daily activities, your body is doing an adequate job of keeping your blood pH somewhere between 7.35 to 7.45, and the foods that you are eating are not causing any wild deviations of your blood pH. [/quote]


      • I think ‘slightly alkaline’ is potentially misleading to non-chemists. Only completely pure water at exactly 25 degrees Celsius is perfectly neutral in the sense of having an exact balance between hydroxide ions and hydrogen ions. We could argue that nothing we come across on a daily basis is ‘neutral’, everything sits to one side or the other of that finely balanced point. Whilst that may be technically true it’s not very helpful, and it results in misconceptions like the one being discussed here (i.e. forget the ‘slightly’ and just hear the ‘alkaline’). For all intents and purposes, anything from just above pH 6 to just under pH 8 is effectively neutral.

        I also think it’s a bit misleading to compare the pH scale to the Richter scale. Yes, they’re both base 10 logarithmic scales, but that’s about their only similarity. On the Richter scale, which is based on amplitude, 0-1.5 is ‘not felt’, whereas on the pH scale that would be extremely acidic. On the pH scale, pH 7 is neutral and ‘harmless’, whereas on the Richter scale 7 is a strong/major earthquake. So yes, I’d rather be in a 6.8 earthquake (strong) rather than a 7.4 (major) too, but I wouldn’t bother much over the difference beween pH 6.8 and pH 7.4 if I spilt it on my hand!

        The statement in your second paragraph I agree with completely, and have said myself many, many, many times.


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