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Is there a buffer at acidic pH? (pH 1 and 2) - (Sep/04/2013 )

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I want to make a buffers at pH 1 and 2. Does any one know of a buffer I can use? I found a protocol which uses HCl and KCl, but I really do not want to use KCl because of my system.

 

Thanks!

-dustbunny000-

Citric acid with HCl will be around 2, lower I don't know.

-hobglobin-

It's really funny that you said that because that is actually what I'm doind right now! I use citrate buffer for a pH 3 solution and I already have the stocks. I do need that pH 1 data point though!

-dustbunny000-

can't you use the ready-made buffers of the ph-meter also for this? there you have pH 1 and 2 and you're sure to have it right.
For pH 1 Sigma-Aldrich says hydrochloric acid / potassium chloride as ingredients.

-hobglobin-

depending on which way you need to resist change in pH (toward more acidic or more basic, buffering is best at pK+ or -1.0 pH unit):

 

pyrophosphate has pK1=0.9; pK2=2.0 you can use it for both pHs

 

phosphoric acid has pK1=1.0

 

oxalic acid pK1=1.2

 

histidine and maleic (not malic) acid both have pK1=1.8

 

aspartic and glutamic acid both have pK1=2.1

 

lysine has pK1=2.2

 

glycine has pK1=2.4

 

let us know if you require any other suggestions

-mdfenko-

Don't know what will you use it for but many polyprotic acids may be used for that. I work with acidophiles and the media itself does not include anything that is added because its buffering properties. Sulfuric-based solutions around pH2 are quite stable regarding the pH. Ferric iron can buffer too, at pH around 2.3

-El Crazy Xabi-

Do you really need a typical buffer made of conjugate base and acid pair? What you need is a solution that resists pH changes - or has a high enough buffering capacity. At low and high pH buffering capacity of a solution of a strong acid (base) is quite often high enough so that you don't need anything else. Google for buffer capacity plot and you'll see what I mean.

-Borek-

Don't know what will you use it for but many polyprotic acids may be used for that. I work with acidophiles and the media itself does not include anything that is added because its buffering properties. Sulfuric-based solutions around pH2 are quite stable regarding the pH. Ferric iron can buffer too, at pH around 2.3

 

 

Do you really need a typical buffer made of conjugate base and acid pair? What you need is a solution that resists pH changes - or has a high enough buffering capacity. At low and high pH buffering capacity of a solution of a strong acid (base) is quite often high enough so that you don't need anything else. Google for buffer capacity plot and you'll see what I mean.

i think there may be some confusion about what buffers are and how they work.

 

here are a couple of publications that will explain buffer theory and practice:


Attached File

Attached File

-mdfenko-

I believe I have quite good grasp about what the buffers are and what they do. As far as I can tell nothing that is written in the documents you have attached contradicts what I wrote (quite the opposite*).

 

Buffer solution is a solution which keeps the pH constant when you add small amounts of acids and/or bases. Typically we achieve this effect by using a solution that contains a conjugate acid/base pair - that guarantees that adding small amounts of acid/base (and neutralizing acid or its conjugate base) doesn't change pH of the solution by much. 

 

Question is - what is important, fact that the solution keeps constant pH, or fact that it contains a conjugate pair? For practical purposes it is the first thing that matters - pH stability. How it is achieved is secondary. Unfortunately, typically buffers are taught by telling students "buffer is a solution containing a conjugate pair", which is just a way of making a secondary characteristic the most important part of the problem. But when you look at numbers it is obvious that the conjugate pairs is not always necessary.

 

Let's say I have a 100 mL of 0.1M acetic acid buffer at pH 4.75. I add 1 mL of 0.1 M HCl. pH drops down from 4.75 to 4.73 - pretty nice buffering effect, pH stays almost constant, that's what we wanted, that's what we use buffers for.

 

Now let's take another solution, 100 mL of 0.1M HCl - with pH of 1.00. I add 1 mL of 0.1M HCl, just like I did previously - and pH doesn't change at all.

 

Nothing strange, after all, I am mixing pH 1.0 solution with pH 1.0 solution, so perhaps I am just trying to cheat and it was accidental, and I will get another result if I will try to add strong base? Let's see.

 

Acetic buffer (identical like the one used before) - but I am adding 1 mL of 0.1 M NaOH. pH changes from 4.75 to 4.77.

 

0.1M HCl, 100 mL, adding 1 mL of 0.1 M NaOH - pH changes from 1.00 to 1.01. See, the change is even lower than it was in the case of solution that contained a buffer! So perhaps 0.1M HCl solution already BEHAVES like a buffer?

 

And that's where the buffering capacity gives an answer. Please check the plot I mentioned in the previous post. It clearly shows that solutions of low or high pH (which means they already contain some strong acid or base) do behave as if they were containing a buffer, so there is no need to add another one, consisting of a conjugate pair. It works only for highly acidic and highly basic solutions, say pH below 2.0 and above 12.0, but when it works - it works.

 

You will rarely see this discussed in the textbooks, as they mostly deal with buffers working in the middle of the pH scale, where the best approach is to use typical buffer consisting of an acid and its conjugate base. Unfortunately, the only book I am 100% sure it contains similar discussion is rater obscure - see it here.

 

*Please note that Stoll and Blanchard paper clearly states on the second page, that as they discuss pH 3-11, they ignore presence of H+ and OH-. You can't do that when you are dealing with pH 2 solution.

 

Note: I ignored ionic strengths of the solutions to not muddy water, but even including it won't change the conclusion.

-Borek-

then it appears that the confusion is based on terminology, specifically "conjugate acid" and "conjugate base".

 

when dealing with acid-base interactions the proton acceptor is referred to as the "conjugate base" and the proton donor is referred to as the "conjugate acid" (see this wikipedia page).

 

so, the examples you give are still dealing with conjugate acids and bases (except your example of adding 0.1M hcl to 0.1M hcl).

 

this discussion is, however, more of an academic exercise than useful.

-mdfenko-
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