An acid-base reaction, according to the Brønsted-Lowry definition, is a transfer of a proton from one molecule or ion to another. When ammonia is dissolved in water, it undergoes the following reversible reaction. In this reaction, the water molecule is donating a proton to the ammonia molecule.
Every Brønsted-Lowry acid-base reaction can be labelled with two conjugate acid-base pairs.
In this response the ferric ion (Fe3+) is performing as a Lewis Acid and the oxalate anion (C2O42-) as a Lewis Base. A Lewis Acid is an electron pair acceptor and a Lewis Base is an electron pair donor. The oxalate anion is donating electrons to the vacant 3d and 4s orbitals on iron.
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