Question

Is Calcium Hydroxide a weak alkali?

Answer 1

A base is a substance that can either accept hydrogen ions (protons) or, more generally, donate a pair of valence electrons. It can be thought of as the chemical opposite of an acid. Strong base is something which is fully ionic.

Complete answer: Calcium hydroxide is a strong base, however less soluble in water. It gets ionized $100\%$ into calcium ions and hydroxide ions.
$Ca{(OH)_2} \to C{a^{2 + }} + 2O{H^ - }$. The pH value of calcium hydroxide is $(11 - 12.5)$. Its $p{K_b}$ value is $1.37$ (First $O{H^ - }$) and $2.43$ (second $O{H^ - }$).
A strong Arrhenius base, like a strong acid, is a compound that ionizes completely or near-completely in solution. Therefore, the concentration of hydroxide ions in a strongly basic solution is equal to that of the undissociated base.
Common examples of strong Arrhenius bases are the hydroxides of alkali metals and alkaline earth metals such as $NaOH$ and $Ca{(OH)_2}$. Strong bases are capable of deprotonating weak acids, very strong bases can deprotonate very weakly acidic $C - H$ groups in the absence of water.
A weak base is a substance that accepts hydrogen ions or, more generally, donate a pair of valence electrons, a weak base does not therefore, fully ionize or completely accept hydrogen ions in an aqueous solution.
A base can either accept protons from water molecules or donate hydroxide ions to a solution. Both actions raise the pH of the solution by decreasing the concentration of ${H^ + }$ ions. The pH of bases in aqueous solution ranges from greater than $7$ to $14$. The formula of pH is: $pH = - {\log _{10}}[{H^ + }]$
The formula for pOH: $pOH = - {\log _{10}}[O{H^ - }]$.
The base dissociation constant, ${K_b}$ is a measure of basicity- the base’s general strength. It is related to acid dissociation constant, ${K_a}$ by the simple relationship $p{K_a} + p{K_b} = 14$, where $p{K_b}$ and $p{K_a}$ are the negative logarithms of ${K_b}$ and ${K_a}$ respectively. ${K_b} = \dfrac{{[B{H^ + }][O{H^ - }]}}{B}$, where B is the base, $[B{H^ + }]$ is its conjugate acid, and $[O{H^ - }]$ is hydroxide ions.

Note:
Smaller $p{K_b}$ values indicate higher values of ${K_b}$, this also indicates a strong base.
Considered ${H_2}O \rightleftharpoons {H^ + } + O{H^ - }$, in the presence of extra hydroxide ions from, say, sodium hydroxide, the equilibrium is still there, but the position of equilibrium has been shifted well to the left according to Le Chatelier’s principle. There will be far fewer hydrogen ions than there are in pure water, but there will still be hydrogen ions present. The pH is a measure of the concentration of these.