4. Consider a titration of a generic weak acid HA with NaOH. The pK, for the wea

Question

4. Consider a titration of a generic weak acid HA with NaOH. The pK, for the weak acid is 4.56. The starting pH is 2.75. The pH at the equivalence point is 8.67. The pH after 100.0 mL of NaOH has been added is 11.11. A. Write out the net reaction for the titration. B. What is the numerical value of K for the reaction? C. Which of the following indicators would work the best to find the endpoint? Indicator 1 - pK 2.55 or Indicator 2 pKa 4.55 or Indicator 3- pKa-6.55 or Indicator 4-pk 8.55 or Indicator 5 -pKa 10.55

Explanation / Answer

A) net reaction:

HA (aq) + OH- (aq) -----------------> H2O (l) + A- (aq)

B)

K = 10^-pKa

K = 10^-4.56

K = 2.75 x 10^-5

C)

indicator -5 is the best . because endpoint at 8.67. the pKa of the indicator more than this 10.55 so this can show immidiate color change once the titration exceeds endpoint

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