Problem: A weak monoprotic acid is titrated with 0.100 M NaOH. It requires 50.0 mL of the NaOH solution to reach the equivalence point. After 25.0 mL of base is added, the pH of the solution is 3.62.Estimate the pKa of the weak acid.

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We are being asked to estimate the pKa of the weak acid after 25.0 mL of the 0.100 M NaOH solution is added and the pH of the solution is 3.62. 

Note: The equivalence point is reached after the addition of 50.0 mL of the 0.100 M NaOH solution.


Since 25.0 mL of 0.100 M NaOH was added, this is before the equivalence point. 


We will calculate the pKa of the weak monoprotic acid using the following steps:

Step 1. Calculate the initial amounts of weak acid and NaOH in moles

Step 2. Write the chemical equation for the reaction between the weak acid and NaOH.

Step 3. Construct an ICF Chart.

Step 4. Calculate pKa.

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Problem Details

A weak monoprotic acid is titrated with 0.100 M NaOH. It requires 50.0 mL of the NaOH solution to reach the equivalence point. After 25.0 mL of base is added, the pH of the solution is 3.62.

Estimate the pKa of the weak acid.

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Weak Acid Strong Base Titrations concept. You can view video lessons to learn Weak Acid Strong Base Titrations. Or if you need more Weak Acid Strong Base Titrations practice, you can also practice Weak Acid Strong Base Titrations practice problems.

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