What is the pH of a solution with 0.01 M of a weak acid with a Ka of 1.0 x 10^-5

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Question: What is the pH of a solution with 0.01 M of a weak acid with a Ka of 1.0 x 10^-5? (2023) 2023

Options:

Correct Answer: 5.00

Exam Year: 2023

Solution:

Using the formula for weak acids, pH = 0.5(pKa - logC) = 0.5(4.00 - log(0.01)) = 5.00.

What is the pH of a solution with 0.01 M of a weak acid with a Ka of 1.0 x 10^-5? (2023) 2023

What is the pH of a solution with 0.01 M of a weak acid with a Ka of 1.0 x 10^-5? (2023) 2023

Step 1: Identify the concentration of the weak acid, which is given as 0.01 M.
Step 2: Calculate the pKa from the given Ka value. The formula is pKa = -log(Ka). Here, Ka = 1.0 x 10^-5, so pKa = -log(1.0 x 10^-5) = 5.00.
Step 3: Use the formula for calculating pH of a weak acid: pH = 0.5(pKa - logC), where C is the concentration of the acid.
Step 4: Substitute the values into the formula. We have pKa = 5.00 and C = 0.01, so pH = 0.5(5.00 - log(0.01)).
Step 5: Calculate log(0.01). Since 0.01 is 10^-2, log(0.01) = -2.
Step 6: Substitute log(0.01) back into the pH formula: pH = 0.5(5.00 - (-2)) = 0.5(5.00 + 2) = 0.5(7.00).
Step 7: Calculate the final pH: pH = 0.5 * 7.00 = 3.50.

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