Question

Methylamine is a weak base that is found in rotting fish and has a Kb of 4.37 x 10-4. Consider titrating a 20.0-mL sample of 0.120 M methylamine with a 0.100 M HCl solution.

a) What is the initial pH of the methylamine solution?

b) What is the pH of the methylamine solution after the addition of 10.0 mL of HCl?

c) How much acid (in mL) must be added to the methylamine solution in order to reach the equivalence point?

d) What is the pH of the solution at the equivalence point?

e) What is the pH of the solution after the addition of 30.0 mL of HCl?

f) Which of the following indicators would be best suited for use in this titration? Explain your answer in 1-2 sentences.

i. Methyl Orange (pKa = 3.7)

ii. Methyl Red (pKa = 5.1)

iii. Bromothymol Blue (pKa = 7)

iv. Phenol Red (pKa = 7.9)

v. Phenolphthalein (pKa = 9.3)

Answer 1