Understanding the relationship between Arrhenius and Brønsted-Lowry definitions of acids and bases is crucial in chemistry. Arrhenius acids are substances that increase the concentration of hydrogen ions (H⁺) in aqueous solutions, while Arrhenius bases produce hydroxide ions (OH^-). For instance, hydrobromic acid (HBr) qualifies as an Arrhenius acid because it dissociates to release H⁺ ions. Simultaneously, it is also a Brønsted-Lowry acid since it donates H⁺ ions in reactions.

On the other hand, sodium hydroxide (NaOH) is classified as an Arrhenius base due to its ability to produce OH^- ions. This OH^- can accept H⁺ ions from surrounding water molecules, thus making NaOH a Brønsted-Lowry base as well.

However, not all Brønsted-Lowry bases are Arrhenius bases. For example, ammonia (NH₃) does not directly produce OH^- ions when dissolved in water. Instead, it accepts H⁺ ions from water, leading to the formation of OH^- ions indirectly. Therefore, ammonia is a Brønsted-Lowry base but does not meet the criteria to be classified as an Arrhenius base.

Conversely, all Brønsted-Lowry acids are considered Arrhenius acids because they donate H⁺ ions, which are inherently present in aqueous solutions. This highlights the broader scope of the Brønsted-Lowry theory compared to the more restrictive Arrhenius definition, allowing for a wider range of substances to be classified as acids or bases.