Question

If the $pH$ of a basic buffer solution is $9.5$. What will be the $pH$ when the concentration of salt present in it is increased four times?

• A. $9.5$
• B. $4$
• C. $8.997$
• D. $9.877$

Answer 1

Answer: (C)

$8.997$

For basic buffer
$pOH=p{K}_b+\log \frac{\left[Salt\right]}{\left[Base\right]}$
Given $pH=9.5$
$\therefore 14-9.5=p{K}_b+\log \frac{\left[Salt\right]}{\left[Base\right]}...\left(1\right)$
When salt concentration increases $4$ times, let $pOH=x$
$\therefore x=p{K}_b+\log \frac{4\left[Salt\right]}{\left[Base\right]}...\left(2\right)$
On subtracting (2) from (1)
$pOH=x=5.1023$
$\therefore newpH=14-x=8.89=8.9$