Friday
October 31, 2014

Homework Help: AP Chemistry

Posted by Christina on Thursday, May 2, 2013 at 12:41am.

CH3NH2(aq)+H2O(l)=>CH3NH3+(aq)+OH-(aq) Kb=4.4 x 10^-4
Methylamine, CH3NH2, is a weak base that reacts with water according to the equation above. A student obtains a 50.0 mL sample of a methylamine solution and determines the pH of the solution to be 11.77.
(a) Write the expression for the equilibrium constant, Kb, for methylamine.
(b) Calculate the molar concentration of OH- in the 50.0 mL sample of the methylamine solution.
(c) Calculate the initial molar concentration of CH3NH2(aq) in the solution before it reacted with water and equilibrium was established.
The 50.0 mL sample of the methylamine solution is titrated with HCl solution of unknown concentration. The equivalence point of the titration is reached after a volume of 36.0 mL of the HCl solution is added. The pH of the solution at the equivalence point is 5.98.
(d) Write the net-ionic equation that represents the reaction that takes place during the titration.
(e) Calculate the concentration of the HCl solution used to titrate the methylamine.
(f) using the axes provided, sketch the titration curve that results from the titration described above. On the graph, clearly label the equivalence point of the titration.

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