Question: Assertion: Aluminum chloride \[(AlC{l_3})\] is a Lewis acid. Reason: Lewis acid donates an electro...

Question

Assertion: Aluminum chloride $(AlC{l_3})$ is a Lewis acid.
Reason: Lewis acid donates an electron to an acceptor.
Which of the following statements is correct?
A.Both assertion and reason are true and the reason is the correct explanation of the assertion.
B.Both assertion and reason are true but the reason is not the correct explanation of the assertion.
C.The assertion is true but the reason is false.
D.The assertion is false but the reason is true.
E.Both assertion and reason are false.

Answer 1

Solution

The criterion for a substance to act as an acid or a base has been a matter of discussion among the chemists for years. Boyle in 1680 said acids were substances that tasted sour and changed the color of the litmus from blue to red. Roulle in 1774 said bases as the substances that tasted bitter, possessed detergent and soapy properties.

Complete answer:
Step 1
G.N. Lewis in 1923 proposed a more fundamental and more general concept of acid and base in terms of electrons. This is the most widely used concept because of its simplicity and wider applications.
Step 2
According to Lewis, a base is a substance that can furnish an electron pair to form a covalent coordinate bond while acid is a substance that has a tendency to accept an electron pair from a base to form a covalent coordinate bond.
Step 3
A Lewis base possesses a lone pair of electrons and acts as an electron-pair donor. The Lewis acid possesses either an incomplete octet or can expand its octet in the available vacant d orbital and thereby acts as an electron acceptor.
Species like $OH^-$ , $Cl^-$ , $CN^-$ , $H_2O$ , $NH_3$ , $ROH$ , $RNH_2$ , etc possess lone pairs of electrons and behave as Lewis base.
Substances like $SO_3$ , $BCl_3$ , $AlCl_3$ , $BF_3$ , $ZnCl_2$ , etc. are examples of Lewis acids. The central atom in these species possesses an incomplete octet or a vacant d orbital and can take a lone pair of electrons.
Step 4
Aluminum is a third-period element therefore has vacant 3d orbitals where it can accept electrons. As $AlC{l_3}$ can accept electrons and form the respective anions so it acts as a Lewis acid.
$AlC{l_3} + C{l^ - }\xrightarrow{{}}AlCl_4^ -$
Hence, the assertion is true but the reason is false and option c) is the correct answer for the given question.

Note:
Lewis’s definition is a wider definition and is applicable for those reactions in which no ions are formed as well as no transference of hydrogen ions and other ions taking place.