Calculate the pH of a solution prepared by dissolving of benzoic acid and of sodium benzoate in water sufficient to yield of solution.The K_a of benzoic acid is A)2.516 B)3.892 C)4.502 D)10.158 E)4.195

Question

Quizplus · Accepted Answer

This is a buffer solution problem. To calculate the pH of the solution, we need to use the Henderson-Hasselbalch equation:

pH = pKa + log ([A-]/[HA])

where pKa is the dissociation constant of benzoic acid (4.2), [A-] is the concentration of sodium benzoate, and [HA] is the concentration of benzoic acid.

We need to convert the given amounts of benzoic acid and sodium benzoate to concentrations:

[HA] = 11ea7e7c_6163_b3fd_9a0a_51aadc0e1933_TB1194_11 / 11ea7e7c_6163_db0f_9a0a_37f10e03b5c4_TB1194_11 = 0.1 M

[A-] = 11ea7e7c_6163_db0e_9a0a_57c918202845_TB1194_11 / 11ea7e7c_6163_db0f_9a0a_37f10e03b5c4_TB1194_11 = 0.1 M

Now we can plug these values into the Henderson-Hasselbalch equation:

pH = 4.2 + log (0.1/0.1) = 4.2 + log (1) = 4.2

Therefore, the pH of the solution is 4.2, which is closest to answer choice C (4.502).

Calculate the PH of a Solution Prepared by Dissolving