Free Acids, Bases and Salts MCQs with Answers

81. What is the correct relation between pH and pKa?

• A. pH = pKa + log[ Acid/Base ]
• B. pH = pKa - log[ Acid/Base ]
• C. pH = pKa - log[ Base/Acid ]
• D. pH = pKa + log[ Base/Acid ]

Explanation: The Henderson-Hasselbalch equation relates pKa and pH. However, it is only an approximation and should not be used for concentrated solutions or for extremely low pH acids or high pH bases. pH = pKa + log ([conjugate base]/[weak acid]) pH = pka + log ([A-] / [HA]) pH is equal to the sum of the pKa value and the log of the conjugate base concentration divided by the weak acid concentration.

82. A buffer solution is that which resists/minimizes the change in:

• A. pOH
• B. pH
• C. pKa
• D. pKb

Explanation: A buffer solution is a solution that can resist a change in pH upon addition of an acidic or basic component. It contains a weak acid and its conjugate base or a weak base and its conjugate acid. The buffer solution minimizes changes in pH because the weak acid or base reacts with any added acid or base, respectively, to maintain the solution's pH within a relatively narrow range. The buffer solution can only resist a change in pH within a certain range, known as the buffer capacity.

83. What will be the pH of a solution of NaOH with a concentration of 10-3 M?

• A. 3
• B. 14
• C. 11
• D. 7

Explanation: pOH of NaOH will be => pOH=- log[OH-]=-log[10-3]= 3 pH + pOH = 14 pH+3=14 pH= 11 As it is numerical, it can have only one possible answer.

84. When ammonium cyanide (NH4CN) salt is dissolved in water the solution will be:

• A. Neutral
• B. Acidic
• C. Basic
• D. Both acidic and basic

Explanation: A solution of NH4CN is alkaline because CN− is more strong (conjugate base) than NH4+ (which is conjugate acid).

85. Choose acids that are showing leveling effect:i) HClO4 ii)HI iii) HCI iv) HF

• A. i & iv
• B. i, iii, & iv
• C. iii & iv
• D. i, ii, & iii

Explanation: Leveling effect or solvent leveling refers to the effect of solvent on the properties of acids and bases. The strength of a strong acid is limited ("leveled") by the basicity of the solvent. Similarly the strength of a strong base is leveled by the acidity of the solvent Thus H2O is a differentiating solvent for HI HCl HClO4.HF is a weak acid so it doesn't show levelling effect.

86. Which of the following is a lewis acid?

• A. CH3OH
• B. AlCl3
• C. NH3
• D. CH3OCH3

Explanation: AlCl3 is a Lewis acid (electron acceptor) since there is a valence shell found in the aluminum atom which enables the compound to accept electrons.

87. The pH of 10-3 M H2SO4 solution is:

• A. 3.0
• B. 2.7
• C. 2.0
• D. 1.5

Explanation: Given pH= 10-3 After ionization, H2SO4 ⇔ 2H+ + SO4- [H+] from H2SO4 = 2x10-3 We know that pH = -log10 [H+] pH = -log10 (2 x 10-3) = 3 - log2 = 3 - 1.414 = 2.69M

88. After the hydrolysis of ester the change in concentration of acid at different intervals is calculated by:

• A. Titration with KMnO4
• B. Titration with Standard Alkali
• C. Distillation
• D. Evaporation of mixture

Explanation: After the hydrolysis of an ester, the change in concentration of acid at different intervals can be calculated by titration. The hydrolysis of an ester produces a carboxylic acid and an alcohol. To determine the concentration of the acid produced, a sample of the reaction mixture can be taken at different intervals and titrated against a standardized solution of a strong base, such as sodium hydroxide. The volume of the base required to neutralize the acid in the sample can be used to calculate the concentration of the acid at that particular interval. Thus, option B is correct.

89. Which one of them is amphoteric in nature?

• A. Lithium oxide
• B. Beryllium oxide
• C. Calcium oxide
• D. Potassium oxide

Explanation: The amphoteric nature is exhibited by B, beryllium oxide (BeO).

90. Which one is a stronger Lewis Base?

• A. Phenol
• B. Aniline
• C. Pyridine
• D. Both (A) & (B) have equal strength

Explanation: Pyridine basicity appears to be less sensitive to the substituent effect in ionic liquids than in water.