Free Acids, Bases and Salts MCQs with Answers

41. Which of the following salts gives a neutral solution?

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

Explanation: All three salts listed (NaCl, NaNO₃, KI) are formed from the reaction of a strong acid and a strong base. The ions of these salts do not hydrolyze water, so their aqueous solutions are neutral.

42. Which of the following aqueous solutions will be basic?

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

Explanation: Sodium carbonate (Na₂CO₃) is the salt of a weak acid (H₂CO₃) and a strong base (NaOH). The carbonate ion (CO₃²⁻) hydrolyzes water to produce OH⁻ ions, making the solution basic.

43. The pH of 10-2 M aqueous solution of sodium hydroxide is:

• A. 14
• B. 10
• C. 12
• D. 13

Explanation: A 10⁻² M NaOH solution has [𝑂𝐻−]=10 −2 So, pOH = 2, and pH = 14 − 2 = 12. Thus, the solution is strongly basic.

44. Strong acid can be involved in a spontaneous reaction which is termed as:

• A. Addition reaction
• B. Substitution reaction
• C. Neutralization reaction
• D. Reversible reaction

Explanation: A strong acid reacts spontaneously with a strong base. This process produces salt and water and releases energy. Such a spontaneous reaction is called a neutralization reaction.

45. The pKa value of acetic acid is:

• A. 1.34
• B. 3.52
• C. 4.76
• D. 2.53

Explanation: The pK of an acid indicates its strength; lower pK means stronger acid. For acetic acid (CH₃COOH), the pKa is experimentally determined to be 4.76. a a This reflects that acetic acid is a weak acid.

46. 'Ka ' for an acid is higher, the stronger is the acid; relate the strength of an acid with 'pKa ' :

• A. Higher pKa , weaker the acid
• B. Lower pKa , stronger the acid
• C. pKa has no relation with acid strength
• D. Both "Higher pKa , weaker the acid" & "Lower pKa , stronger the acid"

Explanation: The acid dissociation constant Ka measures acid strength; higher Ka means a stronger acid. pKa is related to Ka by the formula pKa = −log Ka , so a lower pKa corresponds to a higher Ka. Thus, lower pKa → stronger acid, higher pKa → weaker acid.

47. Which of the following solutions has a pH of zero?

• A. 1 M HCl
• B. 1 M HF
• C. 1 M HNO₃
• D. 1 M CH₃COOH

Explanation: A pH of zero corresponds to a hydrogen ion concentration of [H⁺] = 10⁰ = 1 M. Since HCl is a strong acid, a 1 M HCl solution will fully dissociate to produce a [H⁺] of 1 M.

48. The pH of a solution is 5. The hydroxyl ion concentration in mol·dm⁻³ is:

• A. 10⁻⁵
• B. 10⁻⁹
• C. 10⁵⋅⁵
• D. 10⁻⁷

Explanation: The relationship between pH and pOH is pH + pOH = 14. If the pH is 5, the pOH is 14 - 5 = 9. The hydroxyl ion concentration is [OH⁻] = 10⁻pOH = 10⁻⁹ M.

49. Which is correct about a 1.0 × 10⁻³ M HCl solution & a 1.0 × 10⁻⁵ M HClO₄ solution?

• A. The HCl solution is less acidic than the HClO₄ solution
• B. The HCl solution is 100 times more acidic than the HClO₄ solution
• C. The HClO₄ solution is 100 times more acidic than the HCl solution
• D. None of these

Explanation: Acidity is determined by the H⁺ concentration. Since both are strong acids, the [H⁺] is equal to their molarity. The ratio of concentrations is (1.0 × 10⁻³) / (1.0 × 10⁻⁵) = 100. Thus, the HCl solution is 100 times more concentrated in H⁺ and more acidic.

50. The pH of an aqueous solution is 5.5. The hydroxyl ion concentration in the solution will be:

• A. 10⁻⁸·⁵
• B. 10⁸⋅⁵
• C. 8.5
• D. -8.5

Explanation: The pOH of the solution is 14 - pH = 14 - 5.5 = 8.5. The hydroxyl ion concentration is given by [OH⁻] = 10⁻pOH. Therefore, [OH⁻] = 10⁻⁸.⁵ M.