Question

A solution has a pH of 4.20. Using the relationship between pH and pOH, what is the concentration of OH−?

Answer 1

Answer:  The concentration of $OH^-$ is $1.58\times 10^{-10}$

Explanation:- pH or pOH is the measure of acidity or alkalinity.

pH is defined as negative logarithm of hydrogen ion concentration. pOH is defined as the negative logarithm of hydroxide ion concentration.

The relation between pH and pOH is given as:

$pH+pOH=14$

Given : pH = 4.20

$pOH=14-4.20=9.8$

$pOH=-log[OH^-]$

$9.8=-log[OH^-]$

$[OH^-]=antilog(-9.8)$

$[OH^-]=1.58\times 10^{-10}M$

Answer 2

Answer : The concentration of $OH^-$ ion is, $1.58\times 10^{-10}M$

Solution : Given,

pH = 4.20

First we have to calculate the pOH.

As we know that,

$pH+pOH=14$

$pOH=14-pH$

$pOH=14-4.20$

$pOH=9.8$

Now we have to calculate the concentration of $OH^-$ ion.

$pOH=-\log [OH^-]$

$9.8=-\log [OH^-]$

$[OH^-]=1.58\times 10^{-10}M$

Therefore, the concentration of $OH^-$ ion is, $1.58\times 10^{-10}M$