Question

Aqueous solution of $AlC{{l}_{3}}$ is acidic towards litmus while $NaCl$ is not. The correct reason behind this is: a.) $AlC{{l}_{3}}$ furnishes $O{{H}^{-}}$ ion in the solution.
b.) $AlC{{l}_{3}}$ furnishes ${{H}^{+}}$ ion in the solution
c.) $AlC{{l}_{3}}$furnishes both $O{{H}^{-}}$and ${{H}^{+}}$ in the solution
d.) $AlC{{l}_{3}}$ is the salt of strong base and strong acid

Answer 1

Hint: If the red litmus is changed to blue color then the solution is basic in nature whereas if the color of blue litmus is changed into red color then solution is basic.

Complete answer:
If the acidic effect of any solution towards litmus then there is release of hydrogen ions in the solution and if any solution shows basic effect towards litmus paper then there is release of hydroxide ions. The salt of weak base and strong acid are acidic in nature. The cation of such a salt reacts with water forming a weak base with the release of hydrogen ions ${{H}^ {+}} $ in solution.
The salt of strong base and weak acid are basic in nature. The anions of such a salt react with water forming a weak acid with the release of hydrogen ions $O{{H}^ {-}} $ in solution.
The salt of strong acid and strong base are neutral in nature. They do not hydrolyze.
$AlC{{l}_ {3}} $ that is aluminum chloride is a salt of strong acid and weak base. Therefore, it reacts with water leading to release of in solution making the solution acidic and that’s why it shows acidic behavior towards litmus paper.
Overall reaction happening in solution:
\[A{{l}^ {3+}} +3{{H}_ {2}} O\rightleftharpoons Al{{(OH)} _ {3}} +3{{H}^ {+}} \]
While on the other hand $NaCl$ is a salt but it is a salt of strong acid and strong base. Hydrolysis is not done by this salt in aqueous solution.
Therefore from all the above options, option B is correct as $AlC{{l}_{3}}$ does not furnishes ion in the solution nor $AlC{{l}_{3}}$furnishes both $O{{H}^{-}}$and ${{H}^{+}}$ in the solution and neither $AlC{{l}_{3}}$ is the salt of strong base and strong acid.
The correct reason is $AlC{{l}_{3}}$ furnishes ${{H}^{+}}$ ion in the solution.

Option B is the correct answer.

Note: Aluminum chloride is a salt of weak base and strong acid, so it releases hydrogen ions in solutions which impart change in color to litmus paper whereas sodium chloride is a salt of strong acid and strong base. It does not hydrolysed in aqueous solution. Therefore, it does not produce any change in color to litmus paper.