Question

In the laboratory, a general chemistry student measured the ph of a 0.583 m aqueous solution of acetic acid to be 2.473. use the information she obtained to determine the ka for this acid.

Answer 1

To determine the Ka (acid dissociation constant) for acetic acid (CH3COOH) based on the given pH and concentration, you can use the following steps:

Step 1: Convert the pH to the hydrogen ion concentration ([H+]):

The pH can be converted to [H+] using the formula: [H+] = 10^(-pH).

In this case, [H+] = 10^(-2.473).

Step 2: Calculate the initial concentration of acetic acid ([CH3COOH]):

The concentration of the acetic acid solution is given as 0.583 M.

Step 3: Assume that the dissociation of acetic acid is minimal compared to its initial concentration (due to being a weak acid), and that the change in concentration of acetic acid after dissociation can be neglected.

Step 4: Set up the equation for the dissociation of acetic acid:

CH3COOH ⇌ H+ + CH3COO-

Since the change in concentration of acetic acid can be neglected, the initial concentration of CH3COOH is equal to the concentration of H+ ions formed:

[H+] = [CH3COOH].

Step 5: Substitute the values into the equation for the acid dissociation constant (Ka):

Ka = ([H+][CH3COO-])/[CH3COOH]

Since [H+] = [CH3COOH], the equation simplifies to:

Ka = [H+][CH3COO-]/[H+]^2

Step 6: Substitute the values and solve for Ka:

Ka = ([H+][CH3COO-])/([H+]^2)

= (10^(-2.473))(0.583)/(10^(-2.473))^2

= 1.75 x 10^(-5)

Therefore, the Ka for acetic acid (CH3COOH) based on the given pH and concentration is approximately 1.75 x 10^(-5).