Chemistry 112,  Exam 4

 

1.  Calculate the pH initial, ½ way to the equivalence point and at the equivalence point for the titration of 0.20 M CH3NH2 with 0.20 M HCl(aq).  Sketch the titration curve that results from the titration.  Be sure to label the pH initially, 1/2 way to the equivalence point and at the equivalence point. 

Kb of CH3NH2 = 4.38 x 10-4.

 

3.   20.0 mL of 0.10 M HCl is titrated with 0.0 M NaOH. 

What is the initial pH of the HCl?  What is the pH 1.0 mL past the equivalence point?

 

4.  What is the pH of a buffer made by mixing 0.10 moles of NaClO in 1.0 L of 0.20 M HClO? Ka of HClO  = 2.9 x 10-8.

 

5.  What is the pH of the buffer in question 11 if 0.050 moles of NaOH is added to problem 4?

 

6.  What is the solubility of PbI2?  Ksp = 1.4x10-8

 

7.  Will a precipitate occur when 25 mL of .010 M CaCl2 (aq) is added to 75 mL of .0020 M NaF(aq)  Ksp (CaF2) = 4.0 x 10-11

 

8.  Short Answer.

(A)  Will Mg(OH)2 dissolve better in a solution with pH = 4 or pH = 9? Why?

(B)  Which solution is a buffer

                        HNO3 with KNO3                  or                    HF  with KF?