The Arrhenius Acid and Base Theory of Ionization
In 1884, Swedish Svante Arrhenius established the theory of acid and base based on the ionisation theory. According to Arrhenius, acids are hydrogen-containing compounds that ionize into H+ ions or protons in water, whereas bases are hydroxide compounds that ionize (dissociate) into OH ions. This idea only applies to substances that dissolve in an aqueous solution (or you can say where water is the solvent). It addresses many common acids, bases, and their chemical reactions, although there are other substances with acidic and basic properties that do not suit the Arrhenius idea.
The concept of acids and bases has been defined in a variety of ways. Several scientists have provided several definitions to classify acids and bases, with some conceptions being relatively limited and others being quite broad. Acids and bases are ubiquitous in our daily lives. Every liquid we used besides water was acidic or basic, such as vinegar (contains acetic acid), soft drinks (contains carbonic acid), buttermilk (contains lactic acid), and soap (contains base). Initially, chemicals were classified based on their flavour and their effect on other compounds.
Acids are substances that have a sour taste, a pungent odour, are corrosive, have a pH less than 7 and turn blue litmus red. The neutralisation reaction occurs when acid and alkali mix to produce salt and water. Less acidic or basic are the products than the reactants. It reacts with metals to form hydrogen. The reaction between sodium hydroxide (a base) and hydrochloric acid, for instance, produces sodium chloride (salt) and water.
Acid is a chemical that, upon ionization, creates H+ ions in a water solvent.
Arrhenius Theory of Ionization of Acids
Arrhenius Acid Example
Above is an example to illustrate this concept:
We can observe from the aforementioned reaction that when hydrochloric acid ionizes in water, H+ and Cl– ions are produced. However, the Arrhenius hypothesis stipulates that acid must create H+ ions in water upon ionization, and the aforementioned reaction demonstrates that this is indeed the case. Thus, HCl is acid according to the Arrhenius concept.
On dissociation, acids such as HNO3, HCl, etc. release one proton and are referred to be monoprotic acids. Polyprotic acids are acids such as H2SO4, H3PO4, etc. that contain more than one hydrogen atom and dissociate into more than one H+ ion. Polyprotic acids are not necessarily stronger than monoprotic acids.
A material is said to as an Arrhenius base if it ionizes to form OH– ions in a water solvent.
Arrhenius theory of Ionization of Bases
Arrhenius Base Example
Above is an example to illustrate this concept: In the aforementioned reaction, Na+ and OH– ions are produced when sodium hydroxide is ionized in water. However, the Arrhenius hypothesis stipulates that a base must produce OH– ions in water upon ionization. As we can see from the preceding process, NaOH did indeed form an OH– ion upon ionization in water. So NaOH is a base in the Arrhenius concept.
Arrhenius bases are compounds that enhance the concentration of OH or hydroxide ion in an aqueous solution and contain at least one OH ion in their formula. NaOH (sodium hydroxide), KOH (potassium hydroxide), Ca(OH)2 (calcium hydroxide), Mg(OH)2 (magnesium hydroxide), and NH4OH are typical Arrhenius bases (ammonium hydroxide)
The Arrhenius theory of acid and base (the water-ion system)
Swedish scientist Svante Arrhenius formulated the acid-base hypothesis. It was the first contemporary application of the acid-base concept. This theory is straightforward and practical. According to the Arrhenius theory, acids increase the concentration of H+ or proton in an aqueous solution. The released H+ ion or proton is not a free-floating proton; rather, it combines with the water molecule to create the hydronium ion (H3O+). Examples of Arrhenius acid include HCl (hydrochloric acid), H2SO4 (sulphuric acid), and HNO3 (nitric acid), amongst others.
Amphoteric characteristics of water
The term amphoteric comes from the Greek word Amphi, which means both (acid and base). Amphoteric compounds have the ability to function as either an acid or a base. For example, water (water).
It dissociates into H+ and OH (hydroxide) ions upon ionisation. The presence of H+ indicates an acidic solution, while the presence of OH suggests a basic solution. Considering that water is a neutral chemical. So, it dissociates into H+ and OH ions in equal measure.
The Benefits of the Arrhenius theory
Using this idea to explain:
- acids and bases strength
- The degree to which Arrhenius acid and Arrhenius base break down into H+ ion and hydroxide ion determines their strength.
- The characteristics of acids and bases in water.
- neutralisation of acid through a base reaction
According to the acid-base theory of Arrhenius:
The amphoteric property of water is crucial since the majority of acid-base chemical reactions occur in its presence. Water is a significant amphoteric substance that may function as both an Arrhenius acid and a base.
Defects in the Arrhenius Theory:
This theory states that upon ionization in water, the acid must provide (H+) and the base must yield (OH–). But not all acids and bases were treated according to this theory. This idea has some flaws, some of which are listed below:
- Why are CO2 and SO2 acids and NH3 basic, respectively, if acid gives (H+) and base gives (OH–) on ionization in water?
- We are aware that neither CO2 nor SO2 contain any hydrogen. So, how will they deliver (H+) upon ionization in water?
- NH3 contains no (OH). So, how will it produce (OH–) upon ionization in water?
- It only applies to solutions that use water as a solvent (aqueous solution)