Question

Which of the following statement (s) is (are) correct?
(a) The pH of 1 .0 x 10-8M solution of HCl is 8  
(b) The conjugate base of H2PO-4 is HPOI2-4  
(c) Autoprotolysis constant of water increases with temperature 
(d) When a solution of a weak monoprotic acid is treated against a strong base, at half - neutralisation point pH = (\(\frac{1}{2}\))pK_a.
Choose the correct answer from the the options given below

• A. (A), (B), (C)
• B. (B), (C), (D)
• C. (B), (C)
• D. (A), (D)

Hint:

In weak acid titrations, the half-neutralization point corresponds to pH = pKa.

Answer 1

The Correct Option is B

Statement Analysis:

• (A): Incorrect—The pH of a \( 1 \times 10^{-8} \, \text{M} \) HCl solution is slightly less than 7 because the \( \text{H}^+ \) ions contributed by the water's autoionization must also be considered. The actual pH is influenced by both sources of \( \text{H}^+ \).
• (B): Correct—The conjugate base of \( \text{H}_2\text{PO}_4^- \) is \( \text{HPO}_4^{2-} \), which forms when \( \text{H}_2\text{PO}_4^- \) loses a proton.
• (C): Correct—The autoionization constant of water (\( K_w \)) increases with temperature because water ionizes more as the temperature rises, resulting in an increase in the concentration of \( \text{H}^+ \) and \( \text{OH}^- \).
• (D): Correct—At the half-neutralization point during a titration, the concentration of the acid equals the concentration of its conjugate base. At this point, \( \text{pH} = \text{p}K_a \), as shown by the Henderson-Hasselbalch equation.

Conclusion:

Correct Statements: (B), (C), (D).

Incorrect Statement: (A).