Is there a combination of an acid and a base that when mixed results in a solution that is more basic or more acidic than the initial base or acid, respectively?
If so, do such combinations have a name?
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1$\begingroup$ This is strongly dependent on what you mean by "acid" and "base." $\endgroup$– ZheCommented Apr 7, 2017 at 15:06
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5 Answers
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$\ce{6HF + Al(OH)3 (s) -> H3[AlF6] + 3H2O}$
$\ce{6HCN + Fe(OH)2 (s) -> H4[Fe(CN)6] + 2 H2O}$
$\ce{TlOH + HOCl + H2O -> Tl(OH)3(s) + HCl}$
May be one of these will work. Even if they don't, you should get the idea where to search.
answered Mar 23, 2013 at 18:06
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Technically, you could say this occurs for the formation of Fluoroantimonic acid $\ce{H2FSbF6}$, one of the strongest known acids. It can formed by reacting $\ce{HF}\text{ and }\ce{SbF5}$: $$\ce{2 HF ⇌ H2F+ + F−}$$ $$\ce{SbF5 + F− → SbF6-}$$ One could argue that the acidic character comes from a combination of the instability of the acidic $\ce{H2F+}$ and the very weak base character of $\ce{SbF6-}$
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$\begingroup$ I'd argue that satisfies the question. $\endgroup$ Commented Apr 7, 2017 at 15:32
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If you are talking about mixing acid or base with acid or base then the other answers have summarised it correctly; We can mix two acids to make a super strong acid. (Often Brønsted acid + Lewis Acid).
However if you are asking about mixing acid and base, that will never lead to stronger acid or base. This is because in the genetral reaction:
$$\ce{\text{Strong Acid}+\text{Strong Base} <=>> \text{Weaker Acid} + \text{Weaker Base}}$$
The equilibrium always lies towards the direction of weaker acid and base.
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1$\begingroup$ I think that's the crux here. Are there any exceptions to this rule, as seen in e.g. Tyberius's answer. I've read of others with e.g. cocrystals forming instead of salts, but that's out of the league of my idle curiosity. $\endgroup$ Commented Apr 7, 2017 at 15:32
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2$\begingroup$ There are no exceptions. Terbius is mixing two acids. I will provide more info later. $\endgroup$– KartikCommented Apr 8, 2017 at 1:48
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When you add a Bronsted-Lowry acid to a Bronsted-Lowry base, you always get a weaker Bronsted-Lowry acid and a weaker Bronsted-Lowry base. But you could possibly get a stronger Lewis acid or base. One example of such a reaction involves two chemicals, ordinarily both "acids" , that you probably already have in your laboratory.
What we call "nitric acid" looks like a base in sulfuric acid solvent, reacting as follows:
$2 \ce {H2SO4}+(\ce {O2N}-\ce {OH}) \rightarrow \ce {NO2+}+\ce {H3O+}+2 \ce {HSO4-} $
The nitryl ion, $\ce {NO2+}$, is a powerful Lewis acid or electrophile that does its thing, especially with aromatic substrates. This is the essence of organic nitration.
answered Apr 8, 2017 at 2:32
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NO, adding acid in base is addition of $\ce{H+}$ ions in $\ce{OH-}$ ions which will certainly reduce the concentration of $\ce{OH-}$ ions in solution and solution will become less basic.
As,
$$\mathrm{pH} = 14 - \mathrm{pOH} = 14 + \log_{10}[\ce{OH-}]$$
EDIT:(after further question in comment)
Whatsoever, you say addition of $\ce{H+}$ would be followed by a decrease in concentration of $\ce{OH-}$ due to release of water. In the case of amphoteric oxides, they behave depending on the nature of the medium; in basic pH it will act as an acid. A polyprotic acid will neutralise the base faster and even in case or organic acids the process will be slow (being weak acids).
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1$\begingroup$ Thanks. I have doubts that this is true in all cases; it would be helpful if you provided evidence to support your claim. I suspect there must be cases involving amphoteric substances, polyprotic acids or organic compounds whose products interact. I am sure there must be some example involving ammonia. :) $\endgroup$ Commented Mar 22, 2013 at 14:21