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My initial thought was that the stronger acid will act as an acid and the weaker acid as base like the reaction between $\ce{H2SO4}$ and $\ce{HNO3}$ but in this reaction there is a lone pair available for protonation, what if the lone pair was not present , will the reaction still occur? Is the answer dependent on what the acids exactly are?

FullBridge
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  • Can you give an example of acid where the lone pair is not present? – Ivan Neretin May 21 '19 at 11:24
  • I meant an acid in which lone pair is unavailable like in Ammonium ion(NH4+). – FullBridge May 21 '19 at 11:44
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    OK, then there will be no reaction of this type. – Ivan Neretin May 21 '19 at 11:55
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    Being an acid and ability of acting as base are 2 independent properties. The same for bases and their ability to act as acids. – Poutnik May 21 '19 at 11:59
  • So a stronger acid cannot protonate a weaker one(in general)? – FullBridge May 21 '19 at 12:00
  • You can, but you will need one of the acids as pure solvent; a solvent like water will just absorb the protons. For example, sulfuric acid or hydrochloric acid in glacial acetic acid. If you only want to consider protonation of acids bearing a + charge like ammonium, then this will not exist. – Blaise May 21 '19 at 13:37
  • related https://chemistry.stackexchange.com/questions/112087/why-doesnt-h%e2%82%84o%c2%b2%e2%81%ba-exist – Mithoron May 21 '19 at 17:08
  • @IvanNeretin There could be if strong enough acid is used (and the other "acid" is good enough base). – Mithoron May 21 '19 at 17:28

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In the case of $\ce{HNO3}$ and $\ce{H2SO4}$, the proton from sulphuric acid protonates the $\ce{-OH}$ group of $\ce{HNO3}$ , which gives $\ce{NO2+}$ , $\ce{HSO4-}$ and water. This mixture of nitric acid and sulphuric acid is widely used as a nitrating mixture for nitration of aromatic compounds.

In case of other acid mixtures, no reaction happens, but there is an equilibrium. The stronger acids dissociates almost completely , decreasing the dissociation of the weaker one by common ion effect.

William R. Ebenezer
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user226375
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