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?
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$\begingroup$ Can you give an example of acid where the lone pair is not present? $\endgroup$– Ivan NeretinMay 21, 2019 at 11:24
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$\begingroup$ I meant an acid in which lone pair is unavailable like in Ammonium ion(NH4+). $\endgroup$– FullBridgeMay 21, 2019 at 11:44
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1$\begingroup$ OK, then there will be no reaction of this type. $\endgroup$– Ivan NeretinMay 21, 2019 at 11:55
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1$\begingroup$ Being an acid and ability of acting as base are 2 independent properties. The same for bases and their ability to act as acids. $\endgroup$– PoutnikMay 21, 2019 at 11:59
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$\begingroup$ So a stronger acid cannot protonate a weaker one(in general)? $\endgroup$– FullBridgeMay 21, 2019 at 12:00
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1 Answer
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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.
