Video Transcript
Fill in the blank: In Brønsted–Lowry theory, a base is defined as being blank.
To solve this question, we need to complete the statement to create an accurate definition of a base. The definition needs to correspond to the Brønsted–Lowry theory of acids and bases. This theory, proposed by two scientists, Johannes Brønsted and Thomas Lowry in 1932, expanded the definition of acids and bases to include more substances. In their theory, acids and bases are defined by the roles they play in the transfer of protons or hydrogen ions during a chemical reaction. Our job in this question is to determine if a base gives or receives an H+ ion.
Let’s take a look at the following reaction involving an acid and a base. The chemical equation contains the equilibrium arrow, which means that this is a reversible reaction. For this problem, we will focus only on the forward reaction. Let’s use the following cartoon to help us determine how the transfer of a proton occurs during the reaction. One of the products that forms is the HS– ion. This ion forms when the reactant H2S loses a proton. The other product in the reaction is the NH4+ ion. This ion forms when the reactant NH3 gains a proton.
In summary, we’ve learned that during this reaction, an H+ ion is transferred from H2S to NH3. According to Brønsted–Lowry theory, an acid is a substance that can donate protons, or H+ ions, during a reaction. In this reaction, it’s the reactant H2S that is donating hydrogen ions to NH3. Therefore, we can classify H2S as the acid in this reaction.
In contrast, a base is a substance that accepts protons during a reaction. In this reaction, the NH3 molecule accepts a proton from the H2S molecule. Therefore, we can classify NH3 as a base. In summary, we can say that Brønsted–Lowry theory defines an acid as an H+ donor and a base as an H+ acceptor. We need to add the words an H+ acceptor to the statement to complete the definition. In Brønsted–Lowry theory, a base is defined as being an H+ acceptor.
