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Can I make a buffer using two different acids/bases? For example, adding 1 mole of acetic acid and 1 mole of ammonia?

The only information I can ever find is that I can make a buffer using only an acid (or base) and its conjugate base (or conjugate acid). So, carbonic acid and carbonate, $\ce{H2CO3}$ and $\ce{HCO3-}$.

Why do I need a conjugate acid-base pair and not two random weak acid-base pairs to make a buffer?

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  • $\begingroup$ In your specific case, a combination of acetic acid $\ce{HC2H3O2}$ and ammonium $\ce{NH4+}$ would not work, since both species are acids. $\endgroup$ – Ben Norris Feb 18 '15 at 11:33
  • $\begingroup$ @BenNorris you, sir, are a pedant. I think Nova meant ammonia NH3. Not everyone here is a native English speaker. $\endgroup$ – Level River St Feb 18 '15 at 13:16
  • $\begingroup$ Welcome to chemistry.se! If you have questions about how to beautify your posts, have a look at the help center. Do you want to know more about this site, please take the tour. $\endgroup$ – Martin - マーチン Feb 20 '15 at 3:37
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Yes, having multiple weak acids and/or bases having different pKa values would give buffering capacity in more than one pH range, or over a greater pK range.

There is a term "universal buffer" which refers to a buffer having multiple pKas spaced thoughout the pH ~2-12 range to give some buffering capacity over the enter pH range.

As explained in A Neutral Buffered Standard for Hydrogen Ion Work and Accurate Titrations Which Can be Prepared in One Minute J. Am. Chem. Soc., 1932, 54, pp 1911–1912, ammonium aceate has the property that if it is added to pure water it produces a buffered solution of pH 7.00, accurate to a hundreth of a pH unit.

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In theory you can, but it depends on the way you prepare the buffer.

A buffer solution is prepared by mixing a weak acid (or base) with a strong salt of that acid

For example you can prepare the following buffer in two ways:

$\ce{HOAc + NaOAc}$

1: Mixing directly a solution of the salt with the acid

2: Adding (let's say dropwise) a solution of $\ce{NaOH}$ to the acid. In this case $\ce{NaOAc}$ will be formed in situ.

What you cannot do!

Prepare a buffer by mixing $\ce{HOAc}$ with $\ce{NaCl}$ for example

On the other hand you can mix two different buffers to get a new one with a different pH range like in the case of universal buffers.

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  • $\begingroup$ The $\ce{OAc}$ shorthand is typically used with $\ce{O}$ preceeding the $\ce{Ac}$, unless the connection continues to the right, in which case $\ce{AcONa}$ would be preferred. $\endgroup$ – Jan Jun 14 '16 at 18:53
  • $\begingroup$ Please refrain from readding clutter once it has been edited out. $\endgroup$ – Jan Jun 14 '16 at 19:02
  • $\begingroup$ @Jan I don't see why I can't include that line. Any explanation? $\endgroup$ – Marange Jun 14 '16 at 19:03
  • $\begingroup$ In short: the help centre which includes a note about ‘taglines’. And hope this helps is one of the most generic taglines out there. It does not much to answer the question and is thus perceived as noise and clutter. Check out this tongue-in-cheek meta post and a similar but more earnest meta-post. $\endgroup$ – Jan Jun 14 '16 at 19:14
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    $\begingroup$ @Marange Hi. Thanks for offering the answer. Please see meta.stackexchange.com/questions/2950/… as to why someone was trying to be helpful and remove it. I'm going to leave the tagline in the post for now, but know that this behavior is discouraged for the reasons outlined in that post. Thanks and welcome! $\endgroup$ – jonsca Jun 15 '16 at 0:20

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