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There are examples of acid base chemistry that are consistent with Arrhenius' theory and also with Brønsted Lowry theory. However, some examples do not fit Arrhenius' theory and require the extension to Brønsted Lowry.

Applying Arrhenius' theory, acids produce H⁺ ions in water and alkalis produce OH^- ions in water. This works well for many examples. Can you think of one?

A neutralisation reaction fits Arrhenius theory, for example, HNO₃ + KOH ↓ KNO₃ + H₂O_(l) .

More generally, H+(aq) + OH^- (aq)  ∏  H₂O(l).

However, take a moment to consider, how do acid-base reactions occur in the absence of water?

Watch the following video clip and judge how well this reaction fits Arrhenius' theory.

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What is the reaction?

Ammonia gas reacts with hydrogen chloride gas to form a white precipitate of ammonium chloride.

NH_3(g) + HCl_(g) ↓ NH₄⁺Cl^-_(s)

What do you notice about this acid base reaction?

There are no hydroxide ions. There is no solvent. And there are no hydrogen ions either.

Importantly, in Brønsted Lowry theory, bases do not need to contain OH^- ions. This is a significant extension to Arrhenius' theory.