24 A solution is prepared by adding 100 mL of 0050 MCHsCOOHa

24. A solution is prepared by adding 100 mL of 0.050 MCHsCOOH(aq) to 100 mL of 0.050 M C&HsCOONa;(aq). The solution is stirred and its pH is measured to be 4.20. After 3 drops of 1.0 MNaOH are added to the solution, the pH of the solution is measured and is still 4.20. Which of the following equations represents the chemical reaction that accounts for the fact that base was added but there was no detectable change in pH? (A) H+(aq) + OH-(aq) H2O() (B) H3O+(aq) + NaTaq) NaOH(g) + H2O(/) (C) OH-(aq) + CcH5COOH(aq) H20() + C6H,COO(aq) (D) OH-(aq) C6H,COONa(aq) NaOH(aq) C6H5C00-(aq)

Solution

answer : C )

explanation:

C6H5COOH and C6H5COONa mixture can acct as a buffer . on addition of strong base it react with acid for conjugate base

reaction :

OH- (aq) + C6H5COOH (aq) ----------------------> H2O (l) + C6H5COO- (aq)

C6H5COO- is the part of buffer so there is no change in pH value

so correct answe is option C)