Question

Choose the solution with lowest pH value.
A. $CaC{O_3}$
B. $C{H_3}COONa$
C. $Ca{\left( {OH} \right)_2}$
D. $CaC{l_2}$

Answer 1

Hint: the lower the pH of a solution, the more acidic it is. As pH is the negative logarithm of the concentration of hydrogen ion. The more the hydrogen ions present in the solution, lower is the value of pH.

Complete step by step answer:
As mentioned in the hint, the pH value depends on concentration of hydrogen ions present in a solution. In the pH scale we recall that it comprises numbers from \[1 - 14\] , where in \[1 - 6\] represents an acidic solution. $7$ represents neutral and $8$ to $14$ represents a basic solution.
Since the values of the solution are not given here, we must compare the pH of the solutions based on the types of ions present in the solution.
 For this, we must split the salts given into $2$ their constituent ions. After splitting the ions, combine the ions with either ${H^ + }$ ions or $O{H^ - }$ ions to form their acids and bases.
Upon doing this we realize how strongly acidic the solution is based on the types of acid found. It must be mentioned that the order of strength of acid must be known by you. I will demonstrate the following options in the steps below.
$CaCO_3$ : in this compound (calcium carbonate), we split it to get calcium ions and carbonate ions. We can combine the positive calcium ions with OH- ions and the negative carbonate ions with H+ ions to form, \[Ca(OH)_2\]and\[H_2CO_3\] . Here we should note that, \[{H_2}C{O_3}\] is a weak acid. Therefore, the solution will have basic character.
\[CH_3COONa\] : here the ions formed are, \[CH_3COO - \] and \[Na + .\] .After doing so, we combine with the hydrogen and hydronium ions to form, \[CH_3COOH\]and\[NaOH\] . This comprises weak acid and strong base. Therefore, it has a high pH.
\[Ca\left( {OH} \right)2\] : this salt is basic in nature. There is no need to split it because it is already a base. This will have a higher pH as well.
\[CaCl_2\]: the ions found here will form the acid $HCl$ and the base \[Ca{OH}_2\] . This mixture contains a strong acid $HCl$ , therefore, this will have the lowest pH.

So, the correct answer is “Option D”.

Note:
It is important to remember that the stronger the acid the lesser is the value of pH.
The more the pKa (the negative log of the acid dissociation constant) of an acid the weaker the acid is. That means a strong acid has a lesser value of pKa. It must be mentioned that the order of strength of acid .