Difference Between Alkali and Base

The key difference between alkali and base is that the group 1 elements are categorized as alkali elements whereas any element or compound having basic properties are categorized as a base.

We often use the word alkali interchangeably to address highly basic solutions and alkali metals. In this context, alkali is referred to the alkali metals of group 1 of the periodic table of elements. However, the term base can refer to any element, molecule, ion, etc. that have basic properties.

CONTENTS

1. Overview and Key Difference
2. What is Alkali
3. What is Base
4. Side by Side Comparison – Alkali vs Base in Tabular Form
5. Summary

What is Alkali?

Alkali is a term that we commonly use for the metals in group 1 of the periodic table. These are also known as alkali metals. Although H is also in this group, it is somewhat different; it has a behaviour that is different from other members of this group. Therefore, lithium (Li), sodium (Na), potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr) are members of this group.

Alkali metals are soft, shiny, silvery colour metals. They all have only one electron in their outer shell, and they like to remove this and form +1 cations. When the outer most electrons get excited, it comes back to the ground state while emitting radiation in the visible range. The emission of this electron is easy; thus, alkali metals are very reactive. Further, the reactivity increases down the group 1 of the periodic table.

These metals form ionic compounds with other electronegative atoms. More accurately, the term alkali refers to the carbonate or the hydroxide of an alkali metal. They also have basic properties. They are bitter in taste, slippery, and react with acids, to neutralize them.

What is Base?

Definitions

Various scientists defined “base” differently. Arrhenius defines it as a substance that donates OH- ions to the solution. Bronsted- Lowry defines a base as a substance that can accept a proton. According to Lewis, any electron donor is a base. According to the Arrhenius definition, a compound should have a hydroxide anion and the ability to donate it as a hydroxide ion to be a base. However, according to Lewis and Bronsted- Lowry, there can be molecules, which don’t possess hydroxides but can act as a base. For instance, NH₃ is a Lewis base, because it can donate the electron pair on nitrogen. Likewise, Na₂CO₃ is a Bronsted- Lowry base without hydroxide groups but can accept hydrogens.

Properties

Bases have a slippery soap like feeling and a bitter taste. They react easily with acids producing water and salt molecules. Caustic soda, ammonia, and baking soda are some of the common bases. We can categorize these compounds into two groups, depending on their ability to dissociate and produce hydroxide ions. They are strong and weak bases. Strong bases like NaOH, KOH, can completely ionize in a solution, to give ions. Weak bases like NH₃ partially dissociate and give fewer amounts of hydroxide ions.

Further, K_b is the base dissociation constant. It indicates the ability to lose hydroxide ions of a weak base. To check whether a substance is a base or not we can use several indicators like litmus paper or pH paper. These compounds show a pH value higher than 7, and it turns red litmus to blue.

What is the Difference Between Alkali and Base?

Group 1 metals are referred to as alkali, or more accurately, their carbonates and hydroxides are referred to as alkali. However, they have basic properties; thus, they are a subset of bases. The key difference between alkali and base is that the group 1 elements are categorized as alkali elements whereas any element or compound having basic properties are categorized as a base. Therefore, all alkalis are bases, but not all bases are alkalis. Another significant difference between alkali and base is that the alkali forms ionic salts whereas the bases are necessarily not so.

The below infographic on the difference between alkali and base shows these differences in tabular form.

Summary – Alkali vs Base

We often use the two terms alkali and base interchangeably, but they are two different terms. The key difference between alkali and base is that the group 1 elements are categorized as alkali elements whereas any element or compound having basic properties are categorized as a base.

Reference:

1. Britannica, The Editors of Encyclopaedia. “Alkali.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 14 Jan. 2014. Available here  
2. “Base (Chemistry).” Wikipedia, Wikimedia Foundation, 27 Nov. 2018.  Available here 

Image Courtesy:

1.”Sodium hydroxide image”By Walkerma – Own work, (Public Domain) via Commons Wikimedia  
2.”Ba(OH)2 octahydrate”By Leiem – Own work, (CC BY-SA 4.0) via Commons Wikimedia