Free Acids, Bases and Salts MCQs with Answers

1. All of the following are postulates of Arrhenius theory of ionization except

• A. electrolytes ionize in water to produce cations and anions
• B. ionization is a reversible process
• C. electrical conductivity of a solution of an electrolyte depends on the extent to which the electrolyte ionizes in the solution
• D. strong electrolyte ionize to a greater extent in water

Explanation: The Arrhenius theory of ionization does not specifically address the reversibility of the ionization process. The theory primarily focuses on the ionization of electrolytes in water, leading to the production of ions. It describes the dissociation of electrolytes into ions in aqueous solutions, contributing to the electrical conductivity of the solution.

2. Which of the following aqueous solution will be basic?

• A. NaCl
• B. Na2SO4
• C. Na2CO3
• D. FeCl3

Explanation: When dissolved in water, Na2CO3 undergoes hydrolysis, where water molecules react with the carbonate ion (CO3^2-) to produce hydroxide ions (OH-) and bicarbonate ions (HCO3-).This reaction increases the OH- concentration in the solution, making it basic. The equation for the hydrolysis is:CO3^2- + H2O ⇌ HCO3- + OH-

3. A start of reaction, concentration of reactants are on

• A. Higher side
• B. Lower side
• C. Optimum side
• D. Constant

Explanation: At the start of a reaction, the concentration of reactants is on the higher side. This is because, initially, the reaction has just begun, and the reactants are present in higher concentrations before they start getting consumed and converted into products. As the reaction proceeds, the concentrations of reactants gradually decrease, and the concentrations of products increase.For a generic reaction:Reactant→ProductAt the start of the reaction, the reactant concentration is higher, and as the reaction progresses, the concentration of the reactant decreases while the concentration of the product increases.

4. An acid that can act as an oxidizing, dehydrating and acid-producing agent is

• A. HNO3
• B. H2SO4
• C. H2SO3
• D. H3PO4

Explanation: Sulfuric acid (H2SO4) is an acid that can act as an oxidizing, dehydrating, and acid-producing agent.Oxidizing agent: Sulfuric acid can act as an oxidizing agent under certain conditions. For example, in the presence of concentrated sulfuric acid, it can oxidize organic compounds containing reducing functional groups (e.g., alcohols) to form aldehydes, ketones, or carboxylic acids.Dehydrating agent: Sulfuric acid is a powerful dehydrating agent due to its strong affinity for water. When sulfuric acid reacts with water, it can remove water molecules from other compounds, leading to dehydration reactions. For example, when sulfuric acid reacts with sugar (C6H12O6), it removes water molecules to form carbon (as carbonaceous material) and water.Acid-producing agent: Sulfuric acid is a strong acid and can readily donate protons (H+) in aqueous solution, making it an effective acid-producing agent. In various chemical reactions, sulfuric acid can donate protons to other substances, leading to the formation of conjugate bases and resulting in acidic properties.

5. Which of the following compounds is the strongest Bronsted acid

• A. HCl
• B. H2S
• C. HBr
• D. H20

Explanation: HCl is a strong Bronsted acid because it readily donates a proton (H⁺ ion) when dissolved in water, forming the hydronium ion (H₃O⁺). This dissociation occurs almost completely in aqueous solution.

6. The strongest conjugate base is:

• A. NO₃⁻
• B. Cl⁻
• C. SO₄ ²⁻
• D. CH₃COO⁻

Explanation: The strength of a conjugate base is inversely related to the strength of its acid. Since acetic acid (CH₃COOH) is the weakest acid among the choices, its conjugate base, the acetate ion (CH₃COO⁻), is the strongest.

7. A proton acceptor is a:

• A. Bronsted-Lowry base
• B. Bronsted-Lowry acid
• C. Lewis acid
• D. Lewis base

Explanation: According to the Brønsted-Lowry theory, a base is defined as a substance that can accept a proton (H⁺). Ammonia (NH₃) is a classic example of a proton acceptor.

8. Which one of the following acids has a strong conjugate base?

• A. CH₃COOH
• B. HCl
• C. HNO₃
• D. H₂SO₄

Explanation: There is an inverse relationship between the strength of an acid and its conjugate base. A weak acid will have a strong conjugate base. Since acetic acid (CH₃COOH) is a weak acid, its conjugate base (CH₃COO⁻) is relatively strong.

9. The pH of a 0.001M aqueous solution of NaOH is:

• A. 6
• B. 13
• C. 11
• D. 12

Explanation: NaOH is a strong base, so [OH⁻] = 0.001 M = 10⁻³ M. The pOH is -log[OH⁻] = -log(10⁻³) = 3. The pH is calculated as pH = 14 - pOH = 14 - 3 = 11.

10. The aqueous solution of which one of the following compounds can maintain its pH constant?

• A. CH₃COOH and (NH₄)₂SO₄
• B. NH₄NO₃ and KNO₃
• C. NH₄OH and NH₄Cl
• D. NH₄OH and NaCl

Explanation: A solution that maintains a constant pH is a buffer solution. A basic buffer is formed by mixing a weak base with the salt of that weak base and a strong acid. NH₄OH (a weak base) and NH₄Cl (its salt) form a basic buffer.