Free Acids, Bases and Salts MCQs with Answers

161. Which of the following can be added to a solution of ammonium chloride to get buffer solution?

• A. Sodium hydroxide
• B. Acetic acid
• C. Ammonium hydroxide
• D. Calcium hydroxide & potassium hydroxide

Explanation: A buffer solution is formed when a weak acid and its conjugate base, or a weak base and its conjugate acid are present together in a solution. Ammonium chloride (NH4Cl) contains the ammonium ion (NH4+), which acts as a conjugate acid. To create a buffer, you need a weak base that can pair with this conjugate acid. Ammonium hydroxide (NH4OH) is a weak base and can be added to ammonium chloride to form a buffer solution. Sodium hydroxide, calcium hydroxide, and potassium hydroxide are strong bases, which do not form buffer solutions with ammonium chloride. Acetic acid is a weak acid and does not contribute to forming a buffer with ammonium chloride.

162. The pH of buffer solution is 4.74 on adding 0.1 ml (0.0001M) HCl, the pH of solution will be

• A. 5.2
• B. 5.3
• C. 5.7
• D. 4.74

Explanation: The correct answer is 4.74. A buffer solution has the ability to resist changes in pH upon the addition of small amounts of acid or base. In this question, the addition of 0.1 ml of 0.0001M HCl is a very small amount relative to the buffer capacity, so the pH remains unchanged at 4.74. The other options suggest significant changes in pH, which are not typical for a buffer solution.

163. Which is not true about buffer solution?

• A. The solution resists changes in its pH when small amounts of acid or base are added.
• B. The solution maintains a constant pH under typical conditions.
• C. The solution's pH may or may not change significantly during chemical reactions.
• D. The solution resists changes enough to maintain its pH within a narrow range.

Explanation: Buffer solutions are specially designed to resist changes in their pH levels when small amounts of acids or bases are added. They work by using a weak acid and its conjugate base (or a weak base and its conjugate acid) to neutralize added acids or bases. Therefore, statements that describe the buffer's ability to maintain or resist pH changes are true.Option C is the correct answer because a properly functioning buffer solution should not 'may or may not' change its pH significantly during chemical reactions; instead, it should consistently resist such changes within its capacity.

164. Salt hydrolysis is the reverse of

• A. Redox reaction
• B. Solvation
• C. Neutralization
• D. Hydration

Explanation: Salt hydrolysis is the process where a salt reacts with water to produce an acid and a base, essentially reversing the neutralization process where an acid and a base combine to form a salt and water. In neutralization, the acid donates protons to the base, forming a salt. In hydrolysis, the salt dissociates in water to reform the acid and base. Option A, Redox reactions, involve electron transfer rather than proton transfer, making it unrelated to salt hydrolysis. Option B, Solvation, refers to the interaction between solute and solvent, not the breakdown of salts. Option D, Hydration, involves the addition of water to a molecule, which is distinct from the decomposition process in hydrolysis.

165. The aqueous solution of which of the following salt is basic?

• A. NH₄Cl
• B. NaCl
• C. CH₃COONa
• D. NaNO₃

Explanation: The correct answer is CH₃COONa. When CH₃COONa is dissolved in water, it dissociates into CH₃COO⁻ and Na⁺ ions. The CH₃COO⁻ ion can react with water to form CH₃COOH and OH⁻, leading to a basic solution. In contrast, NH₄Cl forms an acidic solution, while NaCl and NaNO₃ form neutral solutions because they are salts derived from strong acids and strong bases, which do not affect the pH of the solution significantly.

166. The aqueous solution of NH₄CN is

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

Explanation: The aqueous solution of NH₄CN is basic. This is because when NH₄CN is dissolved in water, it dissociates into NH₄⁺ and CN⁻ ions. The NH₄⁺ ion is a weak acid and does not significantly contribute to the acidity of the solution. On the other hand, the CN⁻ ion is the conjugate base of the weak acid HCN and hydrolyzes in water to form OH⁻ ions, making the solution basic. Option B is correct. Option A is incorrect because the presence of CN⁻ ions causes the solution to be basic, not acidic. Option C is incorrect because the solution is not neutral due to CN⁻ hydrolysis. Option D is incorrect because the solution's basic nature is predictable based on the hydrolysis of the CN⁻ ion.

167. Which of the following salt gives neutral solution?

• A. NaCl
• B. NaNO₃
• C. KI
• D. All of the above

Explanation: The correct answer is All of the above. Each of the salts listed (NaCl, NaNO₃, KI) is a product of the neutralization of a strong acid and a strong base. As a result, they dissociate completely in water to form ions that do not affect the pH, thereby resulting in neutral solutions.NaCl is formed from HCl and NaOH, NaNO₃ from HNO₃ and NaOH, and KI from HI and KOH. All of these combinations involve strong acids and bases, thus none of these salts will cause a change in pH when dissolved in water, maintaining neutrality.

168. The solution of FeSO₄ is

• A. Acidic
• B. Basic
• C. Neutral
• D. Amphoteric

Explanation: Iron(II) sulfate, FeSO₄, when dissolved in water, undergoes hydrolysis. The sulfate ion (SO₄²⁻) comes from a strong acid (H₂SO₄), while the Fe²⁺ ion is a moderately strong acid when hydrated. This results in an overall acidic solution due to the release of H⁺ ions. Option A is correct. Option B is incorrect because basic solutions typically arise from salts of weak acids and strong bases, which is not the case here. Option C is incorrect as the solution is not neutral; it is acidic due to the dissociation of FeSO₄. Option D is incorrect because FeSO₄ does not exhibit amphoteric properties.

169. Aqueous solution of sodium phosphate is

• A. Acidic
• B. Basic
• C. Neutral
• D. Amphoteric

Explanation: The aqueous solution of sodium phosphate is basic. This is because sodium phosphate is the salt of a strong base (sodium hydroxide, NaOH) and a weak acid (phosphoric acid, H3PO4). In water, sodium phosphate dissociates to produce hydroxide ions (OH-), making the solution basic. Option A is incorrect because an acidic solution results from the presence of excess hydrogen ions (H+), which is not the case here. Option C is incorrect as a neutral solution has a pH of 7, which sodium phosphate does not achieve. Option D is incorrect because sodium phosphate does not exhibit amphoteric properties in solution.

170. Which of the following is mixed salt?

• A. Na₂SO₄
• B. NaKCO₃
• C. CaCl2
• D. NaCl

Explanation: A mixed salt is one that contains more than one type of cation or anion. In the given options, NaKCO₃ contains both sodium (Na⁺) and potassium (K⁺) cations, making it a mixed salt. In contrast, Na₂SO₄, CaCl2, and NaCl are normal salts, each containing only one type of cation and one type of anion, hence they are not mixed salts.