Listed below are two organic acids and their pK_a values. Calculate the acid dis

Question

Listed below are two organic acids and their pK_a values. Calculate the acid dissociation constant, Ka, for each and indicate which of the two is the stronger acid. HC_7H_5O_2 HC_5H_9O_2 pK_a = 5.03 A sample of an organic compound is added to a mixture of octanol and water. After the mixture has reached equilibrium the concentration of the compound in the octanol later is found to be 2.00 times 10^-3 mol/L. The concentration in the water layer is found to be 8.50 times 10^-5 mol/L. Calculate the octanol/water partition coefficient (LogP) for the compound.

Explanation / Answer

1) Since -

For HC7H5O2 :

pKa = 4.20, Ka = 10-4.20 = 6.30*10-5

For HC5H9O2 :

pKa = 5.03, Ka = 10-5.03 = 9.33*10-6

By using Ka values, we conclude that HC7H5O2 is a stronger acid than HC5H9O2

2) Partition coefficient = 2.00*10-3 / 8.50*10-3 = 0.235

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