Calculate the pH of a solution that is 0.1 M in acetic acid (Ka = 1.8 x 10^-5).

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Question: Calculate the pH of a solution that is 0.1 M in acetic acid (Ka = 1.8 x 10^-5).

Options:

Correct Answer: 3.87

Solution:

Using the formula for weak acids, pH = 0.5(pKa - logC) = 0.5(4.74 - log(0.1)) = 3.87.

Calculate the pH of a solution that is 0.1 M in acetic acid (Ka = 1.8 x 10^-5).

Calculate the pH of a solution that is 0.1 M in acetic acid (Ka = 1.8 x 10^-5).

Step 1: Identify the concentration of acetic acid, which is given as 0.1 M.
Step 2: Find the acid dissociation constant (Ka) for acetic acid, which is 1.8 x 10^-5.
Step 3: Calculate the pKa using the formula pKa = -log(Ka). For Ka = 1.8 x 10^-5, pKa = -log(1.8 x 10^-5) ≈ 4.74.
Step 4: Use the formula for calculating the pH of a weak acid: pH = 0.5(pKa - logC), where C is the concentration of the acid.
Step 5: Substitute the values into the formula: pH = 0.5(4.74 - log(0.1)).
Step 6: Calculate log(0.1), which is -1.
Step 7: Substitute log(0.1) into the equation: pH = 0.5(4.74 - (-1)) = 0.5(4.74 + 1) = 0.5(5.74).
Step 8: Calculate the final pH: pH = 0.5 * 5.74 = 2.87.

Weak Acid Equilibrium – Understanding the dissociation of weak acids and the use of the acid dissociation constant (Ka) to calculate pH.
pKa Calculation – Converting Ka to pKa using the formula pKa = -log(Ka) to facilitate pH calculations.
Logarithmic Functions – Applying logarithmic properties in the context of pH calculations, particularly with concentrations.