You are titrating 75.0mL of a 3.21 M pyridine, C5H5N solution with a 2.63 M hydr

Question

You are titrating 75.0mL of a 3.21 M pyridine, C5H5N solution with a 2.63 M hydrochloric acid solution. A) What is the pH of the pyridine solution before you begin titrating? B) What is the pH after 75.0mL of the hydrochloric acid solution has been added? C) What volume of the hydrochloric acid is needed to reach the equivalence point? D) What is the pH at the equivalence point? E) Suggest a good indicator to use for this titration. Explain why. F) What is the pH after 125.0mL of hydrochloric acid has been added?

Explanation / Answer

Moles CH3NH2 = 10.8 x 1.28 / 1000 = 0.0138
CH3NH2 + HCl >> CH3NH3+ + Cl-
Moles HCl = 0.0138
V = 0.0138 / 0.135 = 0.102 L
Total volume = 0.0108 + 0.102 = 0.113 L
[CH3NH3+] = 0.0138 / 0.113 = 0.122 M
CH3NH3+ + H2O <----> CH3NH2 + H3O+
Kh = Kw / Kb = 2.27 x 10^-11 = x^2 / 0.122-x
x = 1.67 x 10^-6 M
pH = 5.78

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