Question

$\text{A waste water sample contains}{10}^{-5.6}mmol/L$ $ofO{H}^{-}ionsat{25}^{o}C$. The pH of this sample is ?

• A. $5.36$
• B. $8.6$
• C. $5.4$
• D. $8.2$

Answer 1

The correct option is C $5.4$

$\text{Concentration of}O{H}^{-}ion$

$={10}^{-5.6}mmol/L$

$\left[O{H}^{-}\right]={10}^{-5.6}\times {10}^{-3}mol/L$

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

$=-log[{10}^{-5.6}\times {10}^{-3}]$

$=8.6$

We know,

$pH+pOH=14$

$pH=14-8.6$

$=5.4$