Question

A weak acid- strong base titration was performed as follows: 10.00 ml of 0.10 m acetic acid were collected in an erlenmeyer flask, and then diluted to 100 ml with distilled water. after that, two drops of indicator were added. then, the buret was filled with 0.100 m NaOH. the titration was started by slowly adding naoh to acetic acid. (note: the volume of two drops indicator is ignored as it is so tiny compared with 100 ml.) what is the ph of the solution in the erlenmeyer flask after adding 10.20 ml of 0.100m NaOH?

a. 9.80
b. 11.08
c. 10.26
d. 9.90

Answer 1

The pH of the solution after adding 10.20 mL of 0.100 M NaOH to 10.00 mL of 0.10 M acetic acid will be slightly above the equivalence point, which is pH 8.72 for acetic acid. Therefore, the closest answer is (b) 9.80.

Step-by-step explanation:

To determine the pH of the solution in the Erlenmeyer flask after adding 10.20 mL of 0.100 M NaOH to 10.00 mL of 0.10 M acetic acid, one should understand that at the point where 10.00 mL of NaOH has been added, the solution is at the equivalence point. Since acetic acid is a weak acid and NaOH is a strong base, the equivalence point would result in a basic solution. The given reference information specifies that the equivalence point of a titration of acetic acid with NaOH would be at a pH of 8.72. Adding slightly more than the equivalence amount (10.20 mL instead of 10.00 mL), the pH will be higher than 8.72 due to the presence of excess NaOH. Considering this and the options provided, the most reasonable answer would be (b) 9.80 since the pH must be greater than 8.72 but not excessively high, as only a slight excess of NaOH has been added.