Free Acids, Bases and Salts MCQs with Answers

21. Which of the following have almost the same pH?

• A. Blood & egg (white)
• B. Tears & blood
• C. Tears & milk
• D. Milk & egg (white)

Explanation: Both human blood and tears are natural buffer systems that maintain a tightly controlled, slightly alkaline pH. The normal pH of blood is about 7.4, and the pH of tears is also very close to 7.4.

22. The aqueous solution of which of the following can form a buffer solution?

• A. HF & NaF
• B. NH₃ & NH₄Cl
• C. H₂CO₃ & NaHCO₃
• D. All of these

Explanation: A buffer solution consists of a weak acid and its conjugate base, or a weak base and its conjugate acid. All three options represent such conjugate pairs and can therefore form effective buffer solutions.

23. Which one is the weakest base among these?

• A. Aniline
• B. Pyridine
• C. Ammonia
• D. Methylamine

Explanation: Aniline is the weakest base because the lone pair of electrons on its nitrogen atom is delocalized into the benzene ring through resonance. This makes the lone pair less available to accept a proton compared to the other amines.

24. At 40°C, the ionic product of water, Kw , is:

• A. 1.0×10⁻¹⁴
• B. 2.9×10⁻¹⁴
• C. 3.8×10⁻¹⁴
• D. 1.8×10⁻¹⁴

Explanation: The autoionization of water is an endothermic process. According to Le Chatelier's principle, increasing the temperature will shift the equilibrium to the right, increasing the concentrations of H⁺ and OH⁻. This results in a larger K value at higher temperatures; at 40°C, it is approximately 2.9×10⁻¹⁴.

25. Which of the following is called a hydrated proton?

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

Explanation: In aqueous solutions, a free proton (H⁺) does not exist on its own. It is strongly attracted to the lone pairs of a water molecule, forming the H₃O⁺ ion, which is known as the hydronium ion.

26. Which of the following contains malic acid?

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

Explanation: Malic acid is a naturally occurring organic acid that is responsible for the sour taste of many fruits. It is found in high concentrations in apples.

27. A one molar solution is acidic for:

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

Explanation: "Ferric chloride (FeCl₃) is the salt of a weak base (Fe(OH)₃) and a strong acid (HCl). The Fe³⁺ ion hydrolyzes water, producing H⁺ ions and making the solution acidic."

28. Which one of the following salts will not be hydrolyzed?

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

Explanation: NaCl is formed from a strong acid (HCl) and a strong base (NaOH), so its ions are too weak to react with water. Therefore, no hydrolysis occurs, and the solution remains neutral.

29. The salt that gives an acidic aqueous solution is:

• A. CH₃COONa
• B. KNO₂
• C. NH₄NO₃
• D. NaI

Explanation: Ammonium nitrate (NH₄NO₃) is the salt of a weak base (NH₃) and a strong acid (HNO₃). The ammonium ion (NH₄⁺) acts as a weak acid in water, donating a proton and making the solution acidic.

30. The salt which is formed from a weak acid & a weak base is:

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

Explanation: Ammonium acetate (CH₃COONH₄) is formed from a weak acid, acetic acid (CH₃COOH), and a weak base, ammonia (NH₃). Both the cation and anion will hydrolyze in water.