The following buffer was prepared: 50. mL 2.0 M methylamine (CH3NH2) solution an

Question

The following buffer was prepared: 50. mL 2.0 M methylamine (CH3NH2) solution and 50. mL of 2.0 M methylamine hydrochloride (CH3NH3Cl) solution. The Kb for methylamine is 4.4 x 10-4.

Part a) What is the pH of the buffer solution? b) 11.12 b) 10.64 c) 12.32 d) 0.48 e) 5.32 24.

Part b) What is the pH of the resulting solution after adding 100 ml of 1.0 M HCl to the original buffer solution? a) 11.12 b) 10.64 c) 12.32 d) 0.48 e) 5.32 25.

Part c) What is the pH of the resulting solution after adding 200 ml of 1.0 M HCl to the original buffer solution? a) 11.12 b) 10.64 c) 12.32 d) 0.48 e) 5.32 26.

Part d) What is the pH of the resulting solution after adding 50 mL of 1.0 M KOH to the original buffer solution? a) 11.12 b) 10.64 c) 12.32 d) 0.48 e) 5.32 27.

Part e) What is the pH of the resulting solution after adding 100 mL of 1.0 M KOH to the original buffer solution? a) 11.12 b) 10.64 c) 12.32 d) 0.48 e) 5.32

Explanation / Answer

Buffer

2 M x 50 ml = 100 mmol CH3NH2

2 M x 50 ml = 100 mmol CH3NH3Cl

Part a) initial pH b) 10.64

Part b) after 100 ml x 1 M HCl added

pH b) 10.64

Part c) after 200 ml x 1 M HCl added

pH b) 10.64

Part d) after 50 ml x 1 M = 50 mmol KOH added

pH = 10.64 + log(100+50/50) = 11.12

a) 11.12

Part e) pH b) 10.64

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