Science Homework Help

I know the answers to these but can you explain/work out the problems here. I am not sure how to calculate these.

     What is the pH of a 0.20 M aqueous solution of CH3NH2 at 25oC? Kb for CH3NH2 = 4.4 x 10-4 and Ka for CH3NH3+ = 2.3 x 10-11

A)   0.70

B)   2.03

C)    7.00

D)   11.97

E)    13.30

2.     What concentration of an aqueous solution of HBrO2 is required to result in the same pH as a 0.050 M solution of HCl? Ka for HBrO2 = 3.7 x 10-4 and Ka for HCl = 1 x 108

A)   0.0043 M

B)   0.050 M

C)    0.054 M

D)   5.00 M

E)    6.81 M

1.     Determine the Kb value for HAsO42- at 25oC given that for H3AsO4:

Ka1 = 5.0 x 10-3

Ka2 = 8.0 x 10-8

Ka3 = 6.0 x 10-10

A)   1.7 x 10-5

B)   1.3 x 10-7

C)    4.0 x 10-10

D)   6.0 x 10-10

E)    2.0 x 10-12

  Calculate the pH of 1.00 L of solution consisting of 0.50 M CH3COOH and 0.35 M LiCH3COO after 0.150 mol of solid NaOH have been added (assume no change in volume). The Ka of CH3COOH is 1.8×10-5 and the Kb for NaOH is 1 x 107

A)  4.23

B)  4.59

C)  4.74

D)  4.90

E)   5.26

 A diprotic acid, H2A, has the following acid dissociation constants: Ka1 = 1.1 x 10-3 and Ka2 = 2.5 x 10-6. Which combination of species would you use to make a buffer solution whose pH is 3.25?

A)  NaHA / H2A

B)  Na2A / NaHA

C)  H2A / NaHA / Na2A

D)  H2A / Na2A

E)   H2A and its conjugates cannot be used to form a buffer of pH = 3.25