Welcome to the Modern sciences. Today we will discuss the Arrhenius base, theories, reactions and examples. There are three sets of major theories by which acids and bases could be explained: Bronsted Lowry theory, Arrhenius theory and Lewis theory. In this article, we’ll see acids and bases based on the Arrhenius theory. Various compounds have similar characteristics which could be categorized into same groups and members of the same groups could be defined by their general behavior and characteristics. Even though it’s rational to define these chemical compounds in chemical terms; some general characteristics could explain their nature too. For instance, acids would taste sour but bases could taste bitter. Acids turn litmus paper red having a ph under 7 whereas bases turn litmus paper blue being on the ph scale over 7 and so on.
Arrhenius concept: Arrhenius bases and acids:
It was in the late 1800s when the Arrhenius theory, the definitions of acids and bases were introduced by Swedish Scientist Svante Arrhenius originally a physicist and also a chemist in physical science. He identified ions in water when compounds were added to it by observation of electrical conductivity; certain compounds are categorized as acids and bases based on the ions each compound releases after its addition in water.
Arrhenius acids: refers to any chemical agents that increases the concentration of H+ ions upon dissociation in aqueous solution. Thereby, forming hydronium ions (H3O+) when combined with water molecules resulting in polar covalent bond. Let’s take a look at a simple example of the reaction of dissociation for hydrochloric acid, HCl (aq) in water:
HCl(aq)➡H+ (aq) +Cl– (aq)
Even though the above equation doesn’t manifest the exact Arrhenius theory, it’s pretty close to that while showing the primary situation when hydrochloric acid (HCl) is added to water. The reaction allows the H+ ions and Cl- ions to be completely dissociated from the hydrochloric acid (HCl) when dissolved in water, releasing H+ ions and enabling the formation of hydronium ions (H3O+)
HCl (aq) + H2O (l)➡H3O+ (aq) + Cl– (aq)
H+ ions as it’s shown on the equation wouldn’t really exist as such; free H+ ions drifting around in the solution, rather it would form hydronium ions (H3O+) and this is what actually refers to the cation of hydrogen H+ ions. The hydronium ion is positively charged because of the cation of hydrogen forming a polar covalent bond with the oxygen having a positive charge makes the hydronium ion a positively charged ion as well. That’s many textbooks just simply refer the H3O+ ions as H+ ions directly in simple equations.
According to the theory, the concentration of H+ ions would increase and as mentioned above the fact about hydronium ions it can be observed that if H+ ions increases the number of hydronium ions H3O+ forming would also increase. A simple example maybe total dissociation of hydro bromic acid HBr (g) into water generating free H3O+ ions:
Hbr (g) +H2O (l) ➡H3O+ (aq) +Br– (aq)
HBr (g)➡H+ (aq) + Br– (aq)
Normally, either of the equations would be considered accurate to demonstrate the dissociation of Arrhenius acid but the first one is more accurate.
Arrhenius bases: theory and examples:
Arrhenius base are chemical compounds which results in the increase of concentration of (OH–) hydroxide ions upon dissociation in aqueous solution. One of the highly soluble bases is Sodium hydroxide (NaOH) which completely dissociates into Na+ ions and OH– ions when dissolved in water. The following equation shows the dissociation reaction for NaOh:
NaOh (aq)➡Na+ (aq) + OH– (aq)
The above reaction could be implied as an ideal example of an Arrhenius base increasing the concentration of OH– ions in aqueous solution as it dissociates fully.
Group 1 hydroxides such as NaOH, KOH and Group 2 hydroxides such as LiOH and Ba(OH)2 are common Arrhenius bases.
Arrhenius theory: Arrhenius Acid + Arrhenius base reactions:
So far the criteria was to analyse the dissociation of Arrhenius acids and bases with water. What happens when Arrhenius bases and Arrhenius acids are combined?
It gives us the equation, Arrhenius acid +Arrhenius base=water+ salt
The products and explanation of the reaction is actually pretty simple if the basic concept is clear. This is also called neutralization reaction. Let’s get to the most common Arrhenius acid-hydrochloric acid (HCl) and most soluble and common Arrhenius base sodium hydroxide (NaOH) to see the reaction between acid and base .Now what would actually happen if we think about the solutions separately:
For the acidic solution:
HCl (aq) ➡H+ (aq) + Cl– (aq)
The concentration of H+ ions increases for the acidic solution.
For the basic solution:
NaOH (aq)➡ Na+ (aq) + OH– (aq)
The concentration of OH– ions increases for the basic solution.
So when both these solutions are combined the H+ ions and the OH– ions react to form water and the rest of the reactants would form salt. The summation of both equations for the formation of water and salt, results in neutralization reaction between hydrochloric acid and sodium hydroxide:
H+ (aq) + OH–(aq)➡H2O (l)
Na+ (aq) + Cl– (aq)➡NaCl (aq)
HCl (aq) +NaOH (aq)➡H2O (l) +NaCl (aq)
Limitations of Arrhenius theory: the setbacks that led to new theories being developed
This theory is confined to the explanations of acid-base chemistry in aqueous solutions and not any other forms, as reactions could also take place in non-aqueous solvents or between molecules in gaseous phase for which this theory fails to provide comprehensive explanations for which Bronsted Lowry theory is usually more acceptable to Chemists. This theory has many more limitations than the other two. The theory specifically suggests the idea of the presence of H+ ions and OH– ions. For example, if a base is weak and lacks hydroxide ions might as well not be considered a base by Arrhenius definitions, inspite of being capable to produce just the same products and thus, because of setbacks like these newer theories were sought for clearer understanding and explanation of the behavior and nature of acids and bases in new manner.