Could a Bronsted-Lowry acid not be an Arrhenius acid? Explain.
Could someone explain the answer to me?
http://www.chemguide.co.uk/physical/acidbaseeqia/theories.html
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Zareh Darakjian, Ph.D.
University of California
In theory, yes.
Bronsted acid is capable of donating a H^+ to ** any ** other compound, not necessarily water. Arrhenius based his definition on the ability to donate H+ to water. So of you have a substance (solvent) which is a weaker acid than water, then a Bronsted acid will be able to donate an H+ to this substance, but the same acid will not be able to donate an H+ to water...
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(559) 709-2022
Zareh Darakjian, Ph.D.
University of California
Yes, a Bronsted-Lowry acid could be an acid that is not an Arrhenius acid. To understand why, let's first clarify the definitions of these two types of acids:
1. Bronsted-Lowry Acid: This concept defines an acid as a substance that can donate a proton (H+) to another substance.
2. Arrhenius Acid: According to Arrhenius theory, an acid is a substance that, when dissolved in water, increases the concentration of H+ ions.
Now, let's consider an example to explain why not all Bronsted-Lowry acids are Arrhenius acids. A common example is ammonia (NH3). In Bronsted-Lowry theory, ammonia can act as an acid because it can donate a proton to an acceptor. Specifically, it can react with water to donate a proton and form the ammonium ion (NH4+):
NH3 + H2O -> NH4+ + OH-
However, according to Arrhenius theory, an acid should increase the concentration of H+ ions when dissolved in water. Ammonia does not exhibit this behavior because it actually decreases the concentration of H+ ions in water. Instead, ammonia acts as a base in Arrhenius theory because it reacts with water to generate hydroxide ions (OH-).
Since ammonia can donate a proton (H+) according to the Bronsted-Lowry definition of an acid but does not increase the concentration of H+ ions in water as required by the Arrhenius definition, it is considered a Bronsted-Lowry acid but not an Arrhenius acid.
In summary, a Bronsted-Lowry acid can be a type of acid that does not fit the definition of an Arrhenius acid, as there are some substances, like ammonia in this example, that can act as Bronsted-Lowry acids without increasing the concentration of H+ ions in water.