Question

What is the pH value of a solution whose hydroxyl ion concentration is$1\times {{10}^{-2}}M$?

Answer 1

Hint :We know that pH value is related to the concentration of${{H}^{+}}$. And for finding the pH value we have to apply the log formula of finding pH.

Complete answer :
We know that hydrogen ion concentration is more conveniently expressed as pH, which is the logarithm of the reciprocal of the hydrogen ion concentration in gram moles per liter or molarity. Thus, in a neutral solution the hydrogen ion (H+) and the hydroxyl ion (OH−) concentrations are equal, and each is equal to 10−7. A pH of 7 is neutral. A decrease in pH below 7 shows an increase in acidity (hydrogen ions), while an increase in pH above 7 shows an increase in basicity (hydroxyl ions). Each pH unit represents a 10-fold change in concentration. So for finding pH of given solution:
Given that the concentration of hydroxide ion is:
$[O{{H}^{-}}]$= $1\times {{10}^{-2}}M$
And we know that,
$pHvalue=\dfrac{1}{{{\log }_{10}}[{{H}^{+}}]}$ and
$p[O{{H}^{-}}]=\dfrac{1}{{{\log }_{10}}[O{{H}^{-}}]}$
Here concentration of hydroxide ion is given so, first we find $p[O{{H}^{-}}]$
So,
$p[O{{H}^{-}}]=\dfrac{1}{{{\log }_{10}}({{10}^{-2}})}$
$p[O{{H}^{-}}]$= -(-2 x ${{\log }_{10}}(10)$) and we know that ${{\log }_{10}}(10)$=1
$p[O{{H}^{-}}]$=2
Also we know the neutrality of solution that
$p[O{{H}^{-}}]$+$p[{{H}^{+}}]$= 14
By putting the value of $p[O{{H}^{-}}]$
$p[{{H}^{+}}]$ + 2 = 14
$p[{{H}^{+}}]$ = 12

So, the pH value of the given solution is ‘12’. And it is a basic solution.

Note : We know that if the value is pH less than 7 then the solution is acidic if ph value is 7 than solution neutral and if pH is greater than 7 and less than 14 then the solution is acidic. And remember that the log formula of hydroxyl ion doesn’t give direct pH value.