According to Lewis concept, an acid is?

Appeared in: KPSC Staff Nurse - 2015

Explanation

According to the Lewis theory of acids and bases, a Lewis acid is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base.
This is the most general definition of an acid, as it is not limited to substances containing hydrogen.
A classic example is Boron Trifluoride (BF₃), which can accept an electron pair from ammonia (NH₃).

Option A: This is the definition of a Brønsted-Lowry acid. This theory focuses on the transfer of protons (H⁺ ions).
Option B: This is the definition of a Brønsted-Lowry base. It is the counterpart to a Brønsted-Lowry acid.
Option C: This is the definition of a Lewis base. A Lewis base is a substance that donates an electron pair to form a covalent bond.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Definition of Lewis Acid as background academic context rather than a clinical decision trigger.
Understanding acid-base concepts is fundamental in pharmacology. Many drug-receptor interactions involve Lewis acid-base chemistry, where a metal ion in an enzyme (a Lewis acid) binds to a drug molecule (a Lewis base).
Chelation therapy, used for heavy metal poisoning, works on this principle. The chelating agent (e.g., EDTA) is a Lewis base that donates multiple electron pairs to bind strongly to a toxic metal ion (a Lewis acid), allowing it to be excreted.
What if the question asked for a Brønsted-Lowry acid? The correct answer would be 'Proton donor', as this theory defines acids and bases based on the transfer of protons (H+ ions).

How to Approach the Question

First, identify the key term in the question: 'Lewis concept'.
This signals that the question is asking for a specific definition from one of the three major acid-base theories.
Recall the definition for each theory. Lewis theory is the most general and deals with electron pairs.
Differentiate the definitions: Arrhenius (H+/OH- in water), Brønsted-Lowry (proton donor/acceptor), and Lewis (electron pair acceptor/donor).
Match the term 'Lewis acid' to its correct definition: 'electron pair acceptor'.
Eliminate the other options by identifying which theory they belong to (e.g., 'proton donor' is Brønsted-Lowry).

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 69-71

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Attempt every question from this paper in a timed mock, then review the full solution for each one.