Free Acids, Bases and Salts MCQs with Answers

141. 0.1 M HCl has pH = 1.0, it is about 100 times stronger than nitric acid. Then pH of acetic acid will be

• A. 1.3
• B. 2.0
• C. 0.1
• D. 3.0

Explanation: The correct answer is 3.0. Acetic acid is a weak acid, which means it doesn't dissociate completely in water. The pH of a 0.1 M solution of a weak acid like acetic acid is typically around 3.0, reflecting its partial ionization. In contrast, strong acids like HCl dissociate completely, resulting in a lower pH. Therefore, the pH of acetic acid is higher (less acidic) compared to strong acids like HCl.The other options are incorrect because they do not accurately represent the typical pH of a weak acid like acetic acid. Option A (1.3) and Option B (2.0) suggest higher acidity than is true for acetic acid, while Option C (0.1) is outside the typical pH range and misrepresents the logarithmic nature of the pH scale.

142. pH of an aqueous solution is 5.5 the hydroxyl ion conc. in the solution will be

• A. 10−8.5
• B. 108.5
• C. 8.5
• D. −8.5

Explanation: To find the concentration of hydroxyl ions, we first determine the pOH of the solution. Since pH + pOH = 14, we have pOH = 14 - 5.5 = 8.5. The concentration of hydroxyl ions is then given by [OH−] = 10−pOH = 10−8.5. Therefore, option A is correct. Options B and C are numerically and conceptually incorrect, and option D is not a valid expression for ion concentration.

143. Which of the following solution have highest pH?

• A. 0.2 M Ca(OH)2
• B. 0.1 M Na(OH)
• C. 0.1 M HCl
• D. 0.1 M CH3COOH

Explanation: The solution with the highest pH is the one that is most basic. Calcium hydroxide, Ca(OH)2, is a strong base and at 0.2 M concentration, it provides a significantly higher concentration of hydroxide ions compared to 0.1 M NaOH, which is also a strong base but at a lower concentration. Both HCl and CH3COOH are acids, with HCl being a strong acid resulting in a very low pH, and CH3COOH being a weak acid resulting in a higher pH than HCl but still much lower than that of the strong bases. Therefore, 0.2 M Ca(OH)2 has the highest pH among the given options.

144. Which of the solution among the following have highest pH?

• A. 0.1M H2SO4
• B. 0.01M NaOH
• C. 0.01M CH3COONa
• D. 0.1M NaHCO3

Explanation: The correct answer is Option B: 0.01M NaOH. Sodium hydroxide (NaOH) is a strong base, which fully dissociates in water, resulting in a high pH value. In contrast, 0.1M H2SO4 is a strong acid, which significantly lowers the pH. 0.01M CH3COONa (sodium acetate) forms a slightly basic solution due to hydrolysis, but it is much weaker than NaOH. 0.1M NaHCO3 (sodium bicarbonate) is a weak base, offering a pH higher than neutral but still not as high as the strong base NaOH.

145. What is the pOH of the solution if the pKa value of acid is 4.5 & the concentration of salt and acid is 0.1 molar & 0.001 molar respectively

• A. 5.5
• B. 6.5
• C. 7.5
• D. None

Explanation: To find the pOH, first use the Henderson-Hasselbalch equation: pH = pKa + log([salt]/[acid]). Given pKa = 4.5, [salt] = 0.1 M, and [acid] = 0.001 M, the pH = 4.5 + log(0.1/0.001) = 4.5 + 2 = 6.5. Since pH + pOH = 14, the pOH = 14 - 6.5 = 7.5. Therefore, the correct answer is option C. Other options represent miscalculations or misunderstanding of the relationship between pH and pOH.

146. Strong acids give leveling effect in

• A. Protogenic solvent
• B. Protophilic solvent
• C. Aprotic solvent
• D. Organic solvent

Explanation: Strong acids exhibit a leveling effect in protophilic solvents because these solvents are capable of accepting protons. This acceptance of protons causes strong acids to dissociate completely, resulting in the same level of acidity irrespective of the specific strong acid used. Protogenic solvents, on the other hand, donate protons and thus do not level strong acids. Aprotic solvents do not participate in proton exchange and therefore do not cause a leveling effect. Organic solvents can have diverse properties and do not uniformly cause a leveling effect for strong acids.

147. Which of the following can be used as a solvent to distinguish between the K values of strong acids?

• A. Protogenic solvent
• B. Protophilic solvent
• C. Aprotic solvent
• D. Organic solvent

Explanation: The correct answer is Option C: Aprotic solvent. Aprotic solvents are ideal for differentiating the K values of strong acids because they do not participate in proton transfer reactions. This allows for a clearer comparison of the acids' dissociation constants without interference from the solvent.Option A, protogenic solvents, donate protons, which can interfere with measuring the ionization of strong acids.Option B, protophilic solvents, can accept protons, potentially altering the acid's dissociation behavior.Option D, organic solvents, encompass a broad range of chemical properties, and not all are suitable for distinguishing strong acids' K values specifically.

148. Strong base give leveling effect in

• A. Protophilic solvent
• B. Protogenic solvent
• C. Aprotic solvent
• D. Organic solvent

Explanation: The leveling effect is the phenomenon where strong acids or bases appear to have the same strength in a particular solvent due to ionization. In a protogenic solvent, which is capable of donating protons, strong bases are neutralized by proton donation, resulting in a leveling effect. This means that all strong bases will appear to have the same strength as the strongest base that can exist in that solvent. Conversely, protophilic solvents accept protons, and aprotic solvents neither donate nor accept protons, making them unsuitable for providing a leveling effect. Organic solvents vary in their properties and are not defined specifically by their proton donating capabilities.

149. The strength of stronge acids can be distinguished in

• A. Protogenic solvent
• B. Protophilic solvent
• C. Aprotic solvent
• D. Organic solvent

Explanation: The correct option is Protogenic solvent. Protogenic solvents are capable of donating protons, which allows them to effectively measure the strength of strong acids by observing their ability to donate protons in such an environment. This is a key characteristic when distinguishing between strong acids. On the other hand, protophilic solvents accept protons, which is not useful for this purpose. Aprotic solvents neither donate nor accept protons, making them unsuitable for distinguishing acid strength. Lastly, organic solvents do not have a specific property related to proton donation or acceptance, and thus do not assist in distinguishing acid strength effectively.

150. The strength of strong bases can be distinguished in

• A. Protogenic solvent
• B. Protophilic solvent
• C. Aprotic solvent
• D. Organic solvent

Explanation: The correct answer is a protophilic solvent, which can accept protons, thereby enhancing the ionization of strong bases. This allows for a clearer distinction of the strength of different strong bases. Protogenic solvents donate protons, which can neutralize bases rather than distinguish their strength. Aprotic solvents do not interact significantly with protons, making them less effective in this context. Organic solvents encompass a broad range of chemical properties and do not specifically aid in distinguishing the strength of strong bases.