Please choose the write answer

Question

A chemist mixes a 0.20 mol/l solution of a weak base where Kb=3.82*10^-10. The PH OF THIS solution is

a) between 5 and 7

b)between 9 and 12

c) between 7 and 9

d) between 12 and 14

Answer 1

You first need to determine the concentration of OH- from this solution. Using the equilibrium constant expression, you have...

K_b = [BH⁺][OH-]/[B]

Using an ICE chart, you can then set up the expression as follows...

3.82E-10 = x²/[0.20 - x]

When you solve for x (using the approximation 3.82E-10 = x²/0.20 ), you get x = 8.74E-6 = [OH-]

When you take -log [OH-], you get [OH-] = 5.06 = pOH

Now subtract this from 14 and you get 14.00 - 5.06 = 8.94 = pH

so your your answer would be C.