Lithium hydroxide (LiOH) is an alkali metal hydroxide that belongs to the Group 1 metal hydroxide family. LiOH has a molar mass of 24 g/mol and a water-like appearance with no odour.
LiOH is made by reacting lithium metal or lithium hydride (LiH) with water. Around room temperature, it exists as a monohydrate and loses the water of crystallisation at 423 K. (150oC).
2Li + 2H2O → 2LiOH + H2 ↑
The reaction of lithium carbonate with lime is another way for producing LiOH.
Li2CO3 + Ca(OH)2 → 2LiOH + CaCO3
As a result, the question of whether LiOH is a strong base emerges.
Is LiOH a reliable base? Yes, LiOH is a strong base since it totally dissociates into its respective ions, Li+ and OH-, in an aqueous solution, leaving no base in the solution. In addition, acids completely neutralise LiOH, leaving only salt and water. Other characteristics, such as the Li atom’s low ionisation energy, size difference, and electronegativity, weaken the Li-OH bond, allowing it to break easily and generate OH ions in solution. As a result, LiOH is a powerful base.
LiOH also has a pKb of -0.04, making it a strong base.
What is the purpose of LiOH as a base?
There are three criteria for determining if a substance is an acid or a base. The following are the concepts:
- The Arrhenius Principle
An acid is a substance that creates H+ions upon ionisation or dissociation in water, whereas a base is a compound that produces OH ions upon dissociation in water.
Is LiOH a Strong Base?
LiOH is referred to as Lithium hydroxide, which belongs to the family of hydroxides of alkali metals, i.e. Group 1 metal. The molar mass of LiOH is 24 g/mol and the solution has a water-like appearance without any odor.
LiOH can be prepared by reaction of Li metal or LiH, lithium hydride with water. It exists in the monohydrate form at room temperature and loses the water of crystallization at 423 K (150oC).
2Li + 2H2O → 2LiOH + H2 ↑
Another method for the preparation of LiOH is by the reaction of lithium carbonate with lime.
Li2CO3 + Ca(OH)2 → 2LiOH + CaCO3
So now the question arises whether LiOH is a strong base.
So, is LiOH a strong base? Yes, LiOH is considered a strong base because it completely dissociates into respective ions in an aqueous solution giving Li+ and OH- without leaving any base in the solution. Also, LiOH undergoes complete neutralization with acids giving only salt and water. Other factors such as low ionization energy, the difference in size, and electronegativity of the Li atom weakens the Li-OH bond and thus it breaks easily and forms OH ions in the solution. Hence LiOH is a strong base.
Also, the pKb of LiOH is -0.04, which makes it a strong base.
Why is LiOH a Base?
There are three concepts that define whether a compound is an acid or a base. The concepts are as follows:
1. Arrhenius Concept
A compound that on ionization or dissociation in water produces H+ions, is said to be an acid, whereas if the compound dissociates to give OH ions, then it is said to be a base.
LiOH + (aq) ——> Li+ (aq) + OH- (aq)
LiOH is an Arrhenius base because it creates OH ions when it dissociates in aqueous solution.
Bronsted-Lowry Concept No. 2
Accepting or donating the proton is the basis of this notion.
If a compound receives a proton, it is a Bronsted base; if the compound can donate a proton, it is a Bronsted acid.
When a bronsted base absorbs a proton, it produces an acid, which is referred to as the base’s conjugate acid.
Similarly, when a bronsted acid contributes a proton, the conjugate base of the acid is formed.
We can observe from the foregoing reaction that LiOH takes a proton from HCl and is hence a bronsted base.
The concept of Lewis
A Lewis acid takes a pair of electrons, while a Lewis base provides a pair of electrons, according to the Lewis idea.
Lewis acids receive a pair of electrons, making them deficient molecules, whereas Lewis bases can donate a pair of electrons, making them rich in electrons.
LiOH is a Lewis base because it includes OH-, an electron-rich species with three lone pairs of electrons that can donate the lone pair of electrons to an electron-deficient species.
We can conclude that LiOH is a base based on the three ideas outlined above since it can operate as a proton acceptor or electron donor, releasing OH ions in the solution.
How can we tell whether LiOH is a strong or weak base?
Understanding the differences between strong and weak bases can help us determine whether LiOH is a strong or weak base.
Strong Base: A strong base is a chemical that dissociates fully into its ions to give OH ions without leaving any base in a solution. For instance, NaOH, KOH, Ca(OH)2, Ba(OH)2, and so on.
The base totally dissociates into stoichiometric moles of ions.
Weak Base: A weak base partially dissociates into ions, leaving some undissociated base in the solution.
Weak bases, such as NH3, CH3NH2, and NH4OH, leave behind some base in solution rather than stoichiometric moles of ions.
As a result, LiOH is a strong base because it dissociates fully in solution, leaving no undissociated base.
Without leaving any undissociated base, 1 mole of LiOH dissociates fully to give 1 mole of Li+ and 1 mole of OH-.
The OH ions in the solution raise the pH of the aqueous solution, making it basic, but Li+ ions have no effect on the pH and are so called spectator ions.
Because Li+ is a weak conjugate acid of LiOH, it does not undergo reverse reaction and remains in solution as ions.
Furthermore, LiOH has a dissociation constant of less than 1, making it a powerful base. If a base’s Kb is less than 1, it’s a strong base; if the Kbis is larger than 1, it’s a weak base.
Factors affecting alkali metal hydroxides’ basic strength (MOH)
- Low ionisation energies: The ionisation energies of alkali metals are low, and they drop as you move down the group.
Because of the low ionisation energy, the link becomes more polar, weakening metal-oxygen interactions and releasing OH ions.
As the ionisation energy of the metals lowers as the group progresses, the basic strength of alkali metal hydroxides increases.
- Atom size (M): The basic strength of metal hydroxides is also determined by the atom size, M.
The M-OH bond will be weaker as the size of M increases, allowing OH ions to be easily separated.
When a result, as the size of M grows smaller, the basic strength of MOH increases.
- Electronegativities of metal atoms, M and O: The bigger the electronegativity difference between the metal atoms, M and O, the more polar the bond becomes, making it easier to break.
As we know, as an element’s electronegativity falls as it moves down the group, the difference between the electronegativities of the metal atom and O grows.
As a result, the bond between M and O decreases down the group, and the ability to produce OH increases, resulting in an increase in basic strength.
Li and O have electronegativity of 0.98 and 3.44, respectively. For a bond to be polar, the electronegativity difference must be extremely large.
The link weakens as a result of the large electronegativity difference, and LiOH dissociates fully into its ions, making it a strong base.
Although LiOH is the weakest of the alkali metal hydroxides, it is nonetheless a powerful base since it dissociates entirely into its constituent ions.
- LiOH is a white hygroscopic solid. The term “hygroscopic compound” refers to a substance that collects moisture from its environment.
- It is a strong base because it is entirely soluble in water and only sparingly soluble in alcohol.
LiOH’s Chemical Properties
- Because LiOH is a strong base, it combines with acids to neutralise them completely, resulting in salt and water via the double displacement method.
2LiOH + H2SO4 —–> Li2SO4 + 2H2O
- When lithium hydroxide reacts with carbon dioxide, it produces an exothermic reaction.
2LiOH + CO2 ——> Li2CO3 + H2O
- Lithium hydroxide reacts with hydrogen chloride.
LiOH + HCl —–> LiCl + H2O
Lithium Hydroxide’s Applications
- LiOH can be used to make a variety of lithium salts, such as LiCl, LiBr, Li2SO4, and so on.
- LiOH is employed as a coolant in water reactors, as well as in ceramics and some Portland cement.
- LiOH is used in spacecraft and submarines to absorb carbon dioxide (CO2) from the air to keep occupants from suffocating.
- It’s employed in batteries as an electrolyte. Nickel-hydrogen and nickel-cadmium batteries benefit from LiOH.
- Lithium hydroxide is commonly employed in the manufacture of fatty and stearic acid lithium soaps, which are utilised as thickeners in lubricating greases.
In conclusion, we can say that LiOH is a base as it releases OH ions in an aqueous solution, and moreover, it is suggested by the three theories, i.e. Arrhenius, Bronsted-Lowry, and Lewis concept.
And it completely dissociates in the solution which makes it a strong base. The basic strength of the hydroxides depends on the ionization energy, size of the metal atom, and the electronegativity difference between the metal atom and oxygen.
Thus, LiOH is a strong base although it is weaker than the alkali metal hydroxides.