A weak base `(BOH)` with `K_(b) = 10^(-5)` is titrated with a strong acid `(HCl)`, At `3//4` th of the equivalence point, pH of the solution is:

Options

A. `5 + "log"3`
B. `14-5-"log"3`
C. `14-5 + log3`
D. `9.523`.

Answer

B

Explanation

Let the initial no. of equivalents of `BOH` be x
`{:(,BOH+HCl,rarr,BCl+,H_(2)O),("Initial equivalent",x,,0,0),("At"3//4th eqv. pt., x-(3x)/(4),,(3)/(4)x,(3)/(4)x):}`
`= x/4`
Now solution contains `x/4` moles of weak base and `(3x)/(4)` moles of its conjugated acid which is a basic buffer.
`pOH = pK_(b) + "log" (["salt"])/(["Base"]) = 5+ "log" (3x xx 4)/(4 xx x)`
`pH = 14 - 5 - log 3 = 8.523`