Free Acids, Bases and Salts MCQs with Answers

171. Solution of Na₂SO₄ is?

• A. Basic
• B. Acidic
• C. Neutral
• D. Not predictable

Explanation: The solution of Na₂SO₄ is neutral because sodium sulfate is a salt resulting from the neutralization of a strong acid (sulfuric acid, H₂SO₄) and a strong base (sodium hydroxide, NaOH). When dissolved in water, neither H⁺ nor OH⁻ ions are released, leading to a neutral pH. The other options are incorrect because they imply the presence of excess H⁺ or OH⁻ ions, which are not present in this case.

172. The salt which is formed of weak acid & weak base

• A. KCl
• B. KNO₃
• C. CH₃COONH₄
• D. CH₃COONa

Explanation: The correct answer is CH₃COONH₄ because it is a salt formed from the reaction between a weak acid (acetic acid) and a weak base (ammonia). This combination leads to a salt that does not completely dissociate in water, and its pH depends on the relative strengths of the acid and base. In contrast, KCl and KNO₃ are formed from strong acids and strong bases, resulting in neutral salts. CH₃COONa, while involving a weak acid (acetic acid), is paired with a strong base (sodium hydroxide), resulting in a basic salt.

173. The salt giving acidic aqueous solution?

• A. CH₃COONa
• B. KNO₃
• C. NH₄NO₃
• D. NaI

Explanation: NH₄NO₃ dissociates into NH₄⁺ and NO₃⁻ in water. The NH₄⁺ ion can donate a proton to water, increasing the concentration of H⁺ ions in the solution, thus making it acidic. CH₃COONa, KNO₃, and NaI dissociate into ions that do not affect the pH significantly, resulting in neutral or basic solutions. Specifically, CH₃COONa forms a basic solution due to the presence of the acetate ion, a conjugate base of a weak acid. KNO₃ and NaI both form neutral solutions as their ions originate from strong acids and bases.

174. Which one of the following salt will not be hydrolyzed?

• A. NaCl
• B. AlCl₃
• C. Na₂CO₃
• D. CH₃COONa

Explanation: NaCl does not undergo hydrolysis because it is a salt formed from the neutralization of a strong acid (HCl) and a strong base (NaOH). These salts do not influence the pH of the solution, as neither ion is reactive with water. On the other hand, AlCl₃ undergoes hydrolysis because it is derived from Al(OH)₃, a weak base, and HCl, a strong acid. Na₂CO₃ undergoes hydrolysis because it is formed from NaOH, a strong base, and H₂CO₃, a weak acid. CH₃COONa also undergoes hydrolysis as it is formed from a weak acid (CH₃COOH) and a strong base (NaOH).

175. One molar solution is acidic for

• A. KI
• B. CH₃COONH₄
• C. FeCl₃
• D. None

Explanation: The correct answer is FeCl₃. FeCl₃ is formed from a weak base (Fe(OH)₃) and a strong acid (HCl), making the solution acidic due to the hydrolysis of the Fe³⁺ ion, which increases the concentration of H⁺ ions. KI is neutral because it is formed from a strong acid and a strong base. CH₃COONH₄ is generally neutral as it involves a weak acid and a weak base. Thus, None is incorrect because FeCl₃ is indeed acidic.

176. Which of the following contain maleic acid?

• A. Milk
• B. Grape
• C. Apple
• D. Lemon

Explanation: The correct answer is Apple. Apples contain maleic acid, which is responsible for their tartness. Maleic acid is less common in other foods listed, like milk, grapes, and lemons. Milk contains lactic acid, grapes contain tartaric acid, and lemons are known for their citric acid content.

177. Which of the following is not alkali?

• A. NaOH
• B. CaO
• C. Al(OH)₃
• D. All of these

Explanation: The correct answer is Option B: CaO. Calcium oxide (CaO) is not an alkali; it is a basic oxide that reacts with water to form calcium hydroxide (Ca(OH)₂), which is an alkali. Sodium hydroxide (NaOH) is a strong alkali, making Option A incorrect. Aluminum hydroxide (Al(OH)₃) is amphoteric and not classified as an alkali, but it can neutralize acids and bases, so it is not the correct answer either. Option D is incorrect because not all listed substances are non-alkalis, as NaOH is clearly an alkali.

178. Water can behave as an acid in the presence of

• A. Ammonia
• B. Alcohol
• C. Ether
• D. All of these

Explanation: With Ammonia (NH₃):Reaction:H2O+NH3→OH−+NH4+\text{H}_2\text{O} + \text{NH}_3 \rightarrow \text{OH}^- + \text{NH}_4^+H2 O+NH3 →OH−+NH4+ Water donates a proton (acts as an acid).Ammonia accepts a proton (acts as a base).✅ Water behaves as an acid.

179. Which of the following is called hydrated proton?

• A. Oxonium ion
• B. Hydroxonium ion
• C. Hydronium ion
• D. Hydroxyl ion

Explanation: The correct answer is Hydronium ion. When an acid dissolves in water, the hydrogen ion (H+) does not exist freely but associates with a water molecule to form the hydronium ion (H3O+), which is commonly referred to as a hydrated proton.The Oxonium ion is another name for the hydronium ion, but it is not as widely used as 'hydronium ion' for this specific context. The term Hydroxonium ion is incorrect and does not exist in proper chemical nomenclature. The Hydroxyl ion (OH-) is related to bases, not acids, and does not involve a hydrated proton.

180. At 40°C Kw is

• A. 1.0×10⁻¹⁴
• B. 2.8×10⁻¹⁴
• C. 3.8×10⁻¹⁴
• D. 1.8×10⁻¹⁴

Explanation: The ion product of water (Kw) is temperature-dependent. At 40°C, the correct value of Kw is 3.8×10⁻¹⁴. This increase from the standard 1.0×10⁻¹⁴ at 25°C is due to the endothermic nature of water dissociation, meaning it absorbs heat, which shifts the equilibrium to produce more ions. Therefore, Option C is the only accurate representation of Kw at 40°C. Option A reflects the value at 25°C, Option B is a close estimation but slightly low, and Option D underestimates the effect of temperature increase.