50.0 mL of 0.1036 M lactic acid (left) was titrated at 25 degree C with 0.1059 M

Question

50.0 mL of 0.1036 M lactic acid (left) was titrated at 25 degree C with 0.1059 M NaOH to the endpoint. Upon reaching the endpoint another 50.0 mL of lactic acid was added, giving a solution pH of 3.08. a. What is the value of delta G for the dissociation of lactic acid? b. If the enthalpy of dissociation for lactic acid was + 20.3 kJ/mol, what is the entropy of dissociation for lactic acid? c. Qualitatively describe how the value of Ka would be different if propanoic acid (right) had been used instead of lactic acid.

Explanation / Answer

b. T= dH/dS

dH= TdS

= 298x20.3

= 6049.4 KJ/mole

C. Lactic acid is more acidic than propanoic acid since it has EWG(OH), it increases the acidity.

So, it can easily undergo disassociation and Releases proton. Hence disassociation constant is more for lactic acid.

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