Free Acids, Bases and Salts MCQs with Answers

111. Which of the following is Bronsted Lowery acid base reaction?

• A. NH₃ + BF₃ → NH₃BF₃
• B. HCl(aq) + NaOH(aq) → NaCl + H₂O
• C. HCl(g) + NH₃(g) → NH₄⁺ + Cl⁻
• D. All of the above

Explanation: The correct answer is Option C: HCl(g) + NH₃(g) → NH₄⁺ + Cl⁻. This reaction exemplifies a Bronsted-Lowry acid-base reaction because HCl donates a proton to NH₃, making HCl the acid (proton donor) and NH₃ the base (proton acceptor). Option A describes a Lewis acid-base reaction involving electron pair donation, not proton transfer. Option B, while an acid-base reaction, is more representative of an Arrhenius acid-base reaction due to the involvement of hydroxide ions. Option D is incorrect because not all the reactions listed are Bronsted-Lowry acid-base reactions.

112. Which of the following is Lewis acid?

• A. AlCl₃
• B. Ag⁺
• C. BCl₃
• D. All of these

Explanation: The correct answer is 'All of these' because AlCl₃, Ag⁺, and BCl₃ all function as Lewis acids. A Lewis acid is defined as a chemical species that can accept an electron pair. AlCl₃ and BCl₃ have central atoms (Al and B, respectively) that can accept electron pairs due to incomplete octets. Ag⁺, being a positively charged ion, can also accept electron pairs. Thus, all these species can act as Lewis acids.

113. The false statement for a base is

• A. Accept protons
• B. Accept pair of electrons
• C. Have high pH
• D. Have low pK Value

Explanation: The correct answer is Option B: Accept pair of electrons. This statement is false for a base; it is characteristic of a Lewis acid. Bases are generally defined as substances that can donate an electron pair (Lewis base) or accept a proton (Bronsted-Lowry base).Option A: Accept protons is incorrect because accepting protons is a characteristic of acids, not bases.Option C: Have high pH is incorrect because bases do have a high pH, usually above 7, making this statement true for a base.Option D: Have low pK Value is incorrect because a low pK value is indicative of a strong acid, whereas strong bases have high pK values.

114. Which of the following is strongest acid amongst these?

• A. CH₃COOH
• B. H₂S
• C. H₂O
• D. HCN

Explanation: The strongest acid amongst the given options is H₂S, as it dissociates more in water compared to the other options. CH₃COOH is a weak acid because it does not completely dissociate in water. H₂O is neutral and does not act as an acid in typical conditions. HCN is also a weak acid, weaker than H₂S. Therefore, H₂S is the strongest acid among the given choices.

115. The characteristics properties of a base in aqueous solution is due to the presence of

• A. Hydride ions
• B. Hydronium ions
• C. Hydroxide ions
• D. Oxide ions

Explanation: The correct answer is Hydroxide ions. In an aqueous solution, bases dissociate to produce hydroxide ions (OH-), which are responsible for the characteristic properties of basic solutions, such as a slippery feel and a high pH. Option A, hydride ions, are not commonly present in aqueous solutions and are not responsible for basicity. Option B, hydronium ions, are associated with acids, not bases. Option D, oxide ions, are incorrect because in aqueous solution, oxides would typically react with water to form hydroxide ions, not remain as oxide ions themselves.

116. Out of 1000 molecules of acetic acid are_ dissociated into ions.

• A. 13
• B. 15
• C. 17
• D. 11

Explanation: Acetic acid (CH3COOH) is a weak acid, meaning it does not fully ionize in solution. Typically, only about 1-2% of acetic acid molecules dissociate into ions in water. Therefore, out of 1000 molecules, approximately 13 (1.3%) dissociate, making option A correct. Option B (15) and Option C (17) indicate a higher dissociation rate than expected for a weak acid. Option D (11) suggests a lower dissociation rate than the typical range. Hence, option A is the most accurate reflection of acetic acid's dissociation behavior.

117. The species which can act both as Bronsted-Lowery acid & base is

• A. HCO₃⁻
• B. HSO₄⁻
• C. H₂O
• D. All of these

Explanation: Correct Answer: All of them - HCO₃⁻, HSO₄⁻, and H₂O - can act as both Brønsted-Lowry acids and bases.

118. Which of the following is not Bronsted-Lowery base?

• A. H₂O
• B. HCO₃⁻
• C. BF₃
• D. ROH

Explanation: The correct answer is BF₃ because a Bronsted-Lowry base is defined as a substance that can accept a proton (H⁺). BF₃ does not accept protons; instead, it acts as a Lewis acid by accepting electron pairs. Conversely, H₂O, HCO₃⁻, and ROH can all accept a proton, fitting the definition of Bronsted-Lowry bases.

119. Which of the following is not Bronsted-Lowery acid?

• A. NH₄⁺
• B. AlCl₃
• C. H₂O
• D. H⁺

Explanation: The correct answer is AlCl₃. AlCl₃ functions as a Lewis acid by accepting electron pairs, but it does not donate protons, which is the defining characteristic of a Bronsted-Lowry acid. In contrast, NH₄⁺ can donate a proton to become NH₃, H₂O can donate a proton to become OH⁻, and H⁺ is itself a proton, making these substances Bronsted-Lowry acids.

120. Arrhenius & bronsted Lowery definitions have greater similarity in

• A. Base definitions
• B. Acid definitions
• C. Both of these
• D. None of these

Explanation: The correct answer is Acid definitions. Both the Arrhenius and Bronsted-Lowry definitions agree that acids are substances that increase the concentration of hydrogen ions (H⁺) in solution. The Arrhenius definition specifies that acids ionize in water to produce H⁺ ions, while the Bronsted-Lowry definition expands on this by describing acids as proton donors. However, the definitions of bases differ: Arrhenius bases yield hydroxide ions (OH⁻) in solution, whereas Bronsted-Lowry bases accept protons (H⁺). Therefore, only the acid definitions show greater similarity between the two theories.