Free Acids, Bases and Salts MCQs with Answers

191. Which of the following concept is also known as proton-donor acceptor system

• A. Bronsted-Lowry
• B. Lewis
• C. Lux-Flood
• D. Usanovich

Explanation: The correct answer is Bronsted-Lowry. This theory specifically defines acids and bases in terms of their ability to donate or accept protons (H+ ions). This directly relates to the concept of a proton-donor acceptor system. The Lewis theory focuses on the transfer of electron pairs rather than protons. The Lux-Flood concept deals with oxide ions, while the Usanovich theory is a more general system that includes various types of transfer, not limited to protons.

192. Which of the following concept is also known as electron pair-donor acceptor system

• A. Bronsted-Lowry
• B. Lewis
• C. Lux-Flood
• D. Usanovich

Explanation: The correct answer is the Lewis concept, which is known as the electron pair-donor acceptor system. According to Lewis, an acid is a substance that can accept an electron pair, while a base is a substance that can donate an electron pair. The other options do not specifically focus on electron pairs: Bronsted-Lowry involves proton transfer, Lux-Flood involves oxide ions, and Usanovich is a more generalized theory.

193. Bases and reducing agents are electron-gying agents and also called as

• A. Electrolytic
• B. Electrophile
• C. Nucleophile
• D. None of the above

Explanation: Bases and reducing agents are electron-donating species, and they are also known as nucleophiles. Nucleophiles are characterized by their ability to donate electrons to electrophiles in chemical reactions. This is why the term 'nucleophile' fits the description given in the question. On the other hand, electrophiles are electron-accepting species, which is the opposite of what bases and reducing agents do. Electrolytic refers to processes involving electrolysis, which is not directly related to electron donation by bases and reducing agents. Therefore, the correct answer is Nucleophile.

194. Lewis concept explain the formation of

• A. Ionic bond
• B. Covalent bond
• C. Co-ordinate bond
• D. Chemical bond

Explanation: The Lewis concept explains the formation of a co-ordinate bond, where one atom donates an electron pair to another atom without sharing. This type of bond is often referred to as a dative covalent bond. In contrast, an ionic bond involves the transfer of electrons, typically forming between metals and non-metals. A covalent bond involves the sharing of electron pairs between atoms, which is different from the electron donation described by the Lewis concept. The term chemical bond is generic and includes various types of bonds, but the Lewis concept specifically addresses the co-ordinate bond.

195. Lux-Flood concept is a dono-acceptor system of

• A. Proton
• B. Electron pair
• C. Neutron
• D. Oxide ion

Explanation: The Lux-Flood concept defines acids and bases in terms of their ability to donate or accept oxide ions (O2-). According to this concept, a Lux-Flood acid is a substance that donates oxide ions, while a Lux-Flood base is one that accepts them. This is particularly applicable in high-temperature reactions involving metal oxides. The other options are incorrect as they refer to different acid-base theories: protons are involved in the Brønsted-Lowry theory, electron pairs in the Lewis theory, and neutrons do not play a role in any acid-base concepts.

196. According to Usanovich concept a base is defined as any species

• A. Capable of giving up anions
• B. Combining with cations
• C. Neutralizing an acid to give a salt
• D. All of the above

Explanation: The Usanovich concept defines a base as any species that can donate anions, accept cations, or neutralize acids to form a salt. This broad definition includes all the actions described in Options A, B, and C. Option A correctly indicates that a base can donate anions. Option B highlights the acceptance of cations, which is also a characteristic of bases. Option C is valid because neutralizing an acid is a classical behavior of bases. Therefore, Option D is the most comprehensive choice as it includes all these possible actions of a base under the Usanovich concept.

197. According to SHAB, Lewis acid are divided into

• A. Two classes
• B. Three classes
• C. Four classes
• D. None of the above

Explanation: The SHAB (Soft Hard Acid Base) principle categorizes Lewis acids into two main classes: hard acids and soft acids. Hard acids prefer to bond with hard bases, and soft acids prefer soft bases. This classification helps in predicting and understanding the stability and reactivity of compounds. Hence, the correct answer is 'Two classes'. The other options are incorrect because they don't align with the SHAB classification of Lewis acids.

198. According to SHAB concept the Lewis base were classified on the basis of

• A. Charge ion size
• B. Polarization consideration
• C. Electron and coordinating ability
• D. All of the above

Explanation: The SHAB (Soft and Hard Acids and Bases) concept classifies Lewis bases based on multiple criteria: charge ion size, polarization, and electron and coordinating ability. These factors together help predict how bases will interact with acids. Option A, B, and C each highlight one aspect of this classification, but Option D correctly identifies that all these factors are considered in the SHAB concept.

199. The one in which the acceptor atom is of low positive charge, large size and has several outer electrons which can be easily excited is a

• A. Soft Base
• B. Hard Base
• C. Soft Acid
• D. Hard Acid

Explanation: The question describes an acceptor atom that is of low positive charge, large size, and has several outer electrons that can be easily excited. These are characteristic features of a soft acid. Soft acids tend to form more covalent bonds and interact with soft bases. In contrast, hard acids have high positive charge and small size, which does not match the description. Soft and hard bases refer to donor characteristics, not acceptor characteristics.

200. All the strong acids have very close pKa value and they appear to have nearly equal strengths in aqueous solutions. The phenomenon is called as

• A. Levelling effect
• B. Differentiating effect
• C. Levelling solvent
• D. Differentiating solvent

Explanation: The correct answer is Levelling effect. In aqueous solutions, all strong acids dissociate completely, making them appear to have equal strength. This phenomenon is called the levelling effect, where the solvent (water) sets a limit on the observable strength of the acids. The other options describe related concepts: a differentiating effect occurs in solvents that allow for partial dissociation, distinguishing between acid strengths, while levelling and differentiating solvents are terms related to the solvent's properties rather than the phenomenon itself.