Question

1. The pH of 0.070 M aniline (C₆H₅NH₂) is 8.73. What are its K_b and pK_b?

2. What mass of potassium hydrogen sulfate is required to make 309 mL of a solution with a pH of 2.27? (The K_a of HSO₄^? = 0.012.)

3.What is the pK_a of iodic acid if the iodate ion concentration in a 0.058-M solution of HIO₃ is 0.045 M?

--I got the answer 1.457 but it is marking it as wrong and im not sure why.

Doing homework and got stumped on these 3 problems. Please help me.

Answer 1

1. The pH of 0.070 M aniline (C₆H₅NH₂) is 8.73. What are its K_b and pK_b?

Given : pH of aniline = 8.73

Concentration of (C6H5NH2) = 0.070 M

To calculate kb and pkb we set up ICE chart

Reaction of C6H5NH2 with water

           C6H5NH2 (aq) + H2O (l) --->C6H5NH2+ (aq) + OH- (aq)

I           0.070                                              0                          0

C          -x                                                   +x                        +x

E        (0.070-x)                                           x                           x

Ka for above reaction = [C6H2NH2+] [ OH-]/(C6H5NH2]

Kb = x²/ (0.070-x)

We need to find x. From the ICE chart x = [OH-]

We have to find [OH-] by using pH

pH + pOH = 14

pOH = 14