Question

The H⁺ concentration in an aqueous solution at 25 °C is 9.1 × 10⁻⁴. What is [OH⁻]?

Answer 1

Steps:-

• First we calculate pH then pOH then [OH-]

$\\ \tt\rightarrowtail pH=-log[H^+]$

$\\ \tt\rightarrowtail pH=-log[9.1\times 10^{-4}]$

$\\ \tt\rightarrowtail pH=-log9.1-log10^{-4})$

$\\ \tt\rightarrowtail pH=0.95+4$

$\\ \tt\rightarrowtail pH=4.95$

Now

$\\ \tt\rightarrowtail pH+pOH=14$

$\\ \tt\rightarrowtail pOH=14-4.95$

$\\ \tt\rightarrowtail pOH=9.05$

So

$\\ \tt\rightarrowtail -log[OH^-]=9.05$

$\\ \tt\rightarrowtail log[OH^-]=-9.05$

$\\ \tt\rightarrowtail OH^-=10^{-9.05}$

$\\ \tt\rightarrowtail OH^-=8.91\times 10^{-4}$