Free Acids, Bases and Salts MCQs with Answers

251. A solution of NaCl is :

• A. acidic in nature
• B. alkaline in nature
• C. neutral in nature
• D. amphoteric in nature

Explanation: This is the following solution: A solution of NaCl is neutral as both Na+ and Cl- ions are weak conjugate acid and base respectively.

252. Arrange the following in increasing order of acid strength:

• A. CCI3COOH < CHCI₂COOH < CH₂CICOOH < CH3COOH
• B. CHCI2COOH < CH₂CICOOH < CH3COOH < CCI2COOH
• C. CH₂CICOOH < CH3COOH < CCI3COOH < CHCI₂COOH
• D. CH3COOH < CH₂CICOOH < CHCI₂COOH < CCI2COOH

Explanation: Acidity is enhanced by the presence of electron-withdrawing groups. The strength of the acid increases with the number of electron-withdrawing chlorine atoms attached to the alpha-carbon, as they increasingly stabilize the conjugate base through the inductive effect.

253. In alkaline buffer solution containing NH4OH and NH4Cl , if some HCl is added its pH will

• A. increase a little
• B. decrease a little
• C. remains constant
• D. change but cannot be predicted

Explanation: In an alkaline buffer solution with NH4OH and NH4Cl, the NH4OH acts as a base, and NH4Cl serves as its conjugate acid. When a small amount of HCl is added, it reacts with the NH4OH, forming NH4Cl and water. This reaction consumes some of the NH4OH, causing a slight decrease in the concentration of hydroxide ions (OH⁻) and, consequently, a decrease in pH. The buffer's capacity to resist pH changes, however, prevents a significant drop in pH.

254. Ammonia react with borontrifluoride & form coordinate covalent bond with BF₃ in this reaction ammonia donate lone pair of electron to

• A. Vacant sp³ hybrid orbital of boron
• B. Half filled sp³ hybrid orbital of boron
• C. Vacant 2p orbital's of boron
• D. Vacant sp² hybrid orbital of boron

Explanation: The reaction between ammonia and boron trifluoride involves the formation of a coordinate covalent bond, where ammonia donates its lone pair of electrons to boron. In BF₃, boron is sp² hybridized, which means there are three sp² hybrid orbitals and one vacant 2p orbital. The vacant 2p orbital of boron is the one that accepts the lone pair of electrons from ammonia, forming the coordinate bond. Options A and B are incorrect because they refer to sp³ orbitals, which are not present in BF₃. Option D is incorrect because although BF₃ is sp² hybridized, the lone pair is donated to the unhybridized 2p orbital, not a hybrid orbital.

255. 25 ml of a solution of barium hydroxide on titration with a 0.1 molar solution of hydrochloric acid gave a titre value of 35ml. The molarity of barium hydroxide solution was:

• A. 0.14
• B. 0.28
• C. 0.35
• D. 0.07

Explanation: Following is the solution to this question:

256. Compounds which tend to donate electron pair are known as lewis bases or nucleophile. Which one of the following is not a Lewis base?

• A. CH3-NH2
• B. PH3
• C. AlCl3
• D. H2O

Explanation: AlCl3 is Lewis acid which can accept electron pair so it cannot be Lewis base but it is Lewis acid.

257. The smaller the value of Pka:

• A. The weaker the base
• B. The stronger the base
• C. The stronger the acid
• D. None of the above

Explanation: Ka is directly proportional to acidic behaviour.. Ka is inversaly proportional to pKa. The acids having smallest pKA value will be strongest acids. Since its value is smallest of all given options. It is the strongest acid.

258. If Ka value is 10-6, then Kb value is:

• A. 10-4
• B. 10-8
• C. 10-6
• D. 10-10

Explanation: As we know that Ka x Kb = KwKw = 10-14Ka = 10-610-6 x Kb = 10-14Kb = 10-14 / 10-6Kb = 10-14 - (-6)Kb = 10-8

259. K, is acid association constant, large PK,, value for an acid indicates that acid is:

• A. Strong
• B. weak
• C. moderate
• D. water soluble

Explanation: if KA is smaller than pKA is large which means weak acid

260. Which of the following is an acidic salt?

• A. NH4Cl
• B. NaCN
• C. CH,COONa
• D. K,SO,

Explanation: NH4Cl is a strong acidic salt because it form by strong acid HCl and ammonia