Question

$0.15$ mole of pyridium chloride has been added into $500{cm}^3$ of $0.2M$ pyridine solution. Calculate pH and hydroxyl ion concentration in the resulting solution assuming no change in volume.
($K_b$ for pyridine $=1.5\times {10}^{-9}M$)

Answer 1

Concentration of pyridium chloride $=0.15\times 2=0.3M$

$pOH=\log \frac{\left[Salt\right]}{\left[Base\right]}-\log K_b=\log \frac{0.3}{0.2}-\log 1.5\times {10}^{-9}=9$

$pOH=-log\left[O{H}^{-}\right]$

$\Rightarrow \left[{OH}^{-}\right]={10}^{-pOH}={10}^{-9}$

$pH=14-pOH=14-9=5$