Achieve #4 week 2

[Isela Tamayo 3H]

If the Kb of a weak base is 1.7×10−6, what is the pH of a 0.25 M solution of this base? pH=??

Can someone help me with this?

[Divya Hebbar]

First you should write out the equation of a weak base in water:
B + H20 --> HB+ + OH-
Then you can set up an ICE chart for the concentrations (ignoring water)
Plug it into the KB expression : kB= (HB+)(OH-) / (B)
The concentrations of OH and HB+ will be the same so you can simplify to kB= x^2/ (B -x).
Since KB is very small, ignore the x in the denominator and solve for x. Taking the -log of X will give you the pOH, so convert it to pH by subtracting it from 14.