Question

How would you determine if the following salts will form a solution that is acidic, basic, or \[pH\]neutral? $C{{H}_{3}}N{{H}_{3}}CN$, $Fe{{(Cl{{O}_{4}})}_{3}}$, ${{K}_{2}}C{{O}_{3}}$, $C{{H}_{3}}N{{H}_{3}}Cl$,$RbI$

Answer 1

Hint:The \[pH\] of a solution can be determined by the use of concentration of the protons present in the solution.
The \[pH\] of the salt solution can be predicted by going through the acid and bases which were combined for the formation of that salt.

Complete step-by-step answer:In order to determine whether the salts would form a solution of acidic, basic or a neutral \[pH\], we must first understand the basic concepts of acid and bases.
The substances which have higher proton concentration, or the substances which readily liberates protons in aqueous solution are known as acids. Similarly, the substances which liberate hydroxide ions in aqueous solution are called bases.
If in case, the substance does not have any proton or hydroxide ion, there is another definition of acid and base which takes in account the availability of lone pair of electrons. SO, the substances or compounds which can donate electrons, are termed as bases and the ones which accept electrons are called acids.
In order to predict the nature of the solutions of salts, the concentration of the salt solution should be known. An ionic equation could be established in order to predict the acidity, basicity or neutrality of the solution. This is the part where conjugate acid-base pairs come in. A conjugate base of an acid is the part of the acid after removal of one proton from the original compound. If the conjugate base of an acid is stable then the acid would be a strong acid.
Now consider the compounds given in the question one by one.
Methyl ammonium cyanide $C{{H}_{3}}N{{H}_{3}}CN$ is an acidic salt as the $C{{H}_{3}}NH_{3}^{+}$ is a conjugate acid of a weak base methylamine $C{{H}_{3}}N{{H}_{2}}$.
$Fe{{(Cl{{O}_{4}})}_{3}}$ is formed by the combination of strong acid which is per chloric acid and a strong base $Fe{{(OH)}_{3}}$, so it is a neutral salt.
${{K}_{2}}C{{O}_{3}}$ is formed by the combination of strong base potassium hydroxide and carbon dioxide. So, it is basic in nature.
$C{{H}_{3}}N{{H}_{3}}Cl$ is an acidic salt as the $C{{H}_{3}}NH_{3}^{+}$ is a conjugate acid of a weak base methylamine $C{{H}_{3}}N{{H}_{2}}$.

Note:If an acidic salt is dissolved in water the solution acquires an acidic nature and if a basic salt is dissolved in water, the solution becomes basic in nature.
If a salt is formed by the combination of a strong acid and a strong base, the nature of the salt becomes neutral.