A 0.239 g sample of unknown organic base...

A 0.239 g sample of unknown organic base is dissolved in water and titrated with a 0.135 M HCl solution. After the addition of 18.35 mL of acid, a pH of 10.73 is recorded. The equivalence point is reached when a total of 39.24 mL of HCl is added. The base and acid combine in a 1:1 ratio.
(a) What is the molar mass of the organic base?
(b) What is the `K_b` value for the base? The `K_b` value could have been determined very easily if a pH measurement had been made after the addition of 19.62 mL of HCl. Why?

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`(a) 45.12 (b) 4.72 xx 10^(-4)`

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