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Broader definitions of a base, to include substances that exhibit typical basic behaviour as pure compounds or when dissolved in solvents other than water, are given by the Brønsted-Lowry theory and the Lewis theory.
- Lewis Base
Other articles where Lewis base is discussed:...
- Bronsted-Lowry Theory
Bronsted-Lowry theory, a theory stating that any compound...
- Lewis Base
A base is a substance that forms hydroxide ions OH-when dissolved in water. For example, hydrochloric acid (\(\ce{HCl}\)) is an acid because it forms \(\ce{H^{+}}\) when it dissolves in water. \[\mathrm{HCl}(\mathrm{g}) \stackrel{\text { Water }}{\longrightarrow} \mathrm{H}^{+}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq}) onumber\]
Jan 30, 2023 · One of the most applicable theories is the Lewis acid/base motif that extends the definition of an acid and base beyond H + and OH-ions as described by Br ø nsted-Lowry acids and bases. The Brø nsted acid-base theory has been used throughout the history of acid and base chemistry.
A Brønsted–Lowry acid is a substance that donates a hydrogen ion, H +, and a Brønsted–Lowry base is a substance that accepts a hydrogen ion. (The name proton is often used as a synonym for H + because loss of the valence electron from a neutral hydrogen atom leaves only the hydrogen nucleus—a proton.)
- Overview
- Key points
- Introduction
- Arrhenius acids
- Hydrogen or hydronium ions?
- Arrhenius bases
- Acid-base reactions: Arrhenius acid + Arrhenius base = water + salt
- Limitations of the Arrhenius definition
- Summary
Definition of Arrhenius acids and bases, and Arrhenius acid-base reactions
•An Arrhenius acid is any species that increases the concentration of H+ in aqueous solution.
•An Arrhenius base is any species that increases the concentration of OH− in aqueous solution.
•In aqueous solution, H+ ions immediately react with water molecules to form hydronium ions, H3O+ .
•An Arrhenius acid is any species that increases the concentration of H+ in aqueous solution.
•An Arrhenius base is any species that increases the concentration of OH− in aqueous solution.
•In aqueous solution, H+ ions immediately react with water molecules to form hydronium ions, H3O+ .
•In an acid-base or neutralization reaction, an Arrhenius acid and base usually react to form water and a salt.
From the vinegar in your kitchen cabinet to the soap in your shower, acids and bases are everywhere! But what does it mean to say that something is acidic or basic? In order to answer this question, we need to examine some of the theories describing acids and bases. In this article, we will focus on the Arrhenius theory.
The Arrhenius theory of acids and bases was originally proposed by the Swedish chemist Svante Arrhenius in 1884. He suggested classifying certain compounds as acids or bases based on what kind of ions formed when the compound was added to water.
An Arrhenius acid is any species that increases the concentration of H+ ions—or protons—in aqueous solution. For example, let's consider the dissociation reaction for hydrochloric acid, HCl , in water:
HCl(aq)→H+(aq)+Cl−(aq)
When we make an aqueous solution of hydrochloric acid, HCl dissociates into H+ ions and Cl− ions. Since this results in an increase in the concentration of H+ ions in solution, hydrochloric acid is an Arrhenius acid.
Let's say we made a 2M aqueous solution of hydrobromic acid, HBr , which is an Arrhenius acid. Does that mean we have 2M of H+ ions in our solution?
Actually, no. In practice, the positively charged protons react with the surrounding water molecules to form hydronium ions, H3O+ . This reaction can be written as follows:
H+(aq)+H2O(l)→H3O+(aq)
Even though we often write acid dissociation reactions showing the formation of H+(aq) , there are no free H+ ions floating around in an aqueous solution. Instead, there are primarily H3O+ ions, which form immediately when an acid dissociates in water. The following picture illustrates the formation of hydronium from water and hydrogen ions using molecular models:
In practice, most chemists talk about the concentration of H+ and the concentration of H3O+ interchangeably. When we want to be more accurate—and less lazy!—we can write the dissociation of hydrobromic acid to explicitly show the formation of hydronium instead of protons:
HBr(aq)+H2O(l)→H3O+(aq)+Br−(aq) More accuratevs.HBr(aq)→H+(aq)+Br−(aq) Shorter and easier to write!
An Arrhenius base is defined as any species that increases the concentration of hydroxide ions, OH− , in aqueous solution. An example of an Arrhenius base is the highly soluble sodium hydroxide, NaOH . Sodium hydroxide dissociates in water as follows:
NaOH(aq)→Na+(aq)+OH−(aq)
In water, sodium hydroxide fully dissociates to form OH− and Na+ ions, resulting in an increase in the concentration of hydroxide ions. Therefore, NaOH is an Arrhenius base. Common Arrhenius bases include other Group 1 and Group 2 hydroxides such as LiOH and Ba(OH)2 .
[Wait, aren't most metal hydroxides insoluble?]
Note that depending on your class—or textbook or teacher—non-hydroxide-containing bases may or may not be classified as Arrhenius bases. Some textbooks define an Arrhenius base more narrowly: a substance that increases the concentration of OH− in aqueous solution and also contains at least one unit of OH− in the chemical formula. While that doesn't change the classification of the Group 1 and 2 hydroxides, it can get a little confusing with compounds such as methylamine, CH3NH2 .
When methylamine is added to water, the following reaction occurs:
When an Arrhenius acid reacts with an Arrhenius base, the products are usually water plus a salt. These reactions are also sometimes called neutralization reactions. For example, what happens when we combine aqueous solutions of hydrofluoric acid, HF , and lithium hydroxide, LiOH ?
If we think about the acid solution and base solution separately, we know the following:
•An Arrhenius acid increases the concentration of H+(aq) :
HF(aq)⇌H+(aq)+F−(aq)
•An Arrhenius base increases the concentration of OH−(aq) :
LiOH(aq)→Li+(aq)+OH−(aq)
The Arrhenius theory is limited in that it can only describe acid-base chemistry in aqueous solutions. Similar reactions can also occur in non-aqueous solvents, however, as well as between molecules in the gas phase. As a result, modern chemists usually prefer the Brønsted-Lowry theory, which is useful in a broader range of chemical reactions. The ...
•An Arrhenius acid is any species that increases the concentration of H+ in aqueous solution.
•An Arrhenius base is any species that increases the concentration of OH− in aqueous solution.
•In aqueous solution, H+ ions immediately react with water molecules to form hydronium ions, H3O+ .
•In an acid-base or neutralization reaction, an Arrhenius acid and base usually react to form water and a salt.
Jun 19, 2021 · In chemistry, a base is a substance that reacts with acids to form a salt and which releases hydroxide ions, accepts protons, or donates electrons in aqueous solution. Learn about the properties of bases and see examples of bases and their uses.
In chemistry, acids and bases have been defined differently by three sets of theories: One is the Arrhenius definition defined above, which revolves around the idea that acids are substances that ionize (break off) in an aqueous solution to produce hydrogen (\(H^+\)) ions while bases produce hydroxide (\(OH^-\)) ions in solution.
