Using the Brønsted-Lowry concept of acids and bases, identify the Brønsted-Lowry acid and base in each of the following reactions: HS - (aq) + H2O (l) →H2S (aq) + OH - (aq) (CH3) 3N (g) + BCl3 (g) → (CH3) 3NBCl3 (s)

A Brønsted-Lowry acid is any species capable of donating a proton (H + ).

A Brönsted-Lowry base is a substance capable of winning or accepting a proton (H + ).

Then there is a transfer of protons that requires the presence of a proton donor, that is, an acid and a base that accepts them. Thus, the acid-base reaction is one in which the acid transfers a proton to a base.

In the first case you have:

HS⁻ + H₂O → H₂S + OH⁻

You can see that the HS⁻ has become H₂S. This indicates that it has accepted a proton (H⁺), so, according to the definitions seen, it is a Brønsted-Lowry base.

H₂O has become OH⁻. As it has an H + less proton, it is possible to say that it has donated said proton, so it is a Brønsted-Lowry acid.

When an acid donates a proton, this acid is called a conjugate base. On the contrary, when a base receives a proton it is known as conjugate acid. This is called conjugate acid-base pairs. And this is what occurs in this case.

In the other case you have:

(CH₃) ₃N (g) + BCl₃ (g) → (CH₃) ₃NBCl₃ (s)

In this case there is no transfer of a proton from an acid to a base. So this reaction cannot be explained by the Brønsted-Lowry theory.