URGENT due tomorrow pls

(a) From the given, we can find out the Kb value of benzylamine as follows:

Kb = 10-14/Ka

= 2.222 × 10-5

Then, after 12.0 mL of acid is added, no. of moles of HCl added = 0.05 × 0.012 = 6 × 10-4 moles and therefore 6 × 10-4 moles of benzylamine have been reacted also, forming 6 × 10-4 moles of salt.

So, no. of moles of benzylamine remained = 0.0319 × 0.05 - 6 × 10-4 = 9.95 × 10-4 moles

Therefore at this moment, the concentration ratio between the alkali and the salt is:

[salt]/[alkali] = 6/9.95 = 0.603

By definition, Kb = [salt][OH-]/[alkali]

2.222 × 10-5 = 0.603 × [OH-]

[OH-] = 3.685 × 10-5 M

pOH = 4.43

pH = 9.57

(b) Using similar method as (a):

After 30 mL of acid is added, no. of moles of HCl added = 0.05 × 0.030 = 0.0015 moles and therefore 0.0015 moles of benzylamine have been reacted also, forming 0.0015 moles of salt.

So, no. of moles of benzylamine remained = 0.0319 × 0.05 - 0.0015 = 9.5 × 10-5 moles

Therefore at this moment, the concentration ratio between the alkali and the salt is:

[salt]/[alkali] = 0.0015/(9.5 × 10-5) = 15.79

By definition, Kb = [salt][OH-]/[alkali]

2.222 × 10-5 = 15.79 × [OH-]

[OH-] = 1.407 × 10-6 M

pOH = 5.85

pH = 8.15