How would I determine Ka? 2. Prepare a graph of the volume of NaOH added to vs.

Question

How would I determine Ka?

2. Prepare a graph of the volume of NaOH added to vs. the pH of the solution. Ensure that all axis are properly labeled. Attach the graph to the data sheet. From the graph, determine the volume of NaOH required to reach the equivalence point of the titration. Annotate this value on the graph and record the value below. 3. Vol NaOH at eq. pt. 1.2 m Calculate the volume of NaOH required to reach the half equivalence point. Annotate this value on the graph and record the value below. 4. Vol NaOH at half eq. pt. 710 m From the graph, what is the pH at the half equivalence point? Annotate this value on the graph and record the value below. 5. pH at half eq. pt.39 6. Using the values above, what is the K, of your unknown acid? 2 7. Based on the K, that you calculated, what is the identity of the unknown acid you analyzed? Unknown acid identity:

Explanation / Answer

Solution:- At half equivalence point, pH = pKa

the pH at half equivalence point is given as 3.92, it means the pKa is 3.92.

pKa = - log Ka

taking antilog to both sides..

Ka = 10-pKa

Ka = 10-3.92 = 0.000120 or 1.20 x 10-4

There would be a list given for the acids along with their Ka values. Select the one that has this calculated Ka value. The acid would be a weak acid like Lactice acid.

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