Question

The pH of a solution containing $ 0.1 $ N NaOH solution is:
(A) 1
(B) $ {10^{ - 1}} $
(C) 13
(D) $ {10^{ - 13}} $

Answer 1

Hint: pH of a solution is the potential of hydrogen and can be defined as the negative logarithm of the concentration of hydrogen ions. pH can express the acidity or alkalinity of a solution. We shall first convert the normality into molarity and then find the pOH and thus it pH.

Formula Used: $ pH = - \log \left[ {{H^ + }} \right] $

Complete step by step solution:
NaOH is a strong base and can completely dissolve in the water giving out species of $ {\text{N}}{{\text{a}}^{\text{ + }}} $ and $ {\text{O}}{{\text{H}}^{\text{ - }}} $ . Hence, the normality of NaOH is equal to the molarity of the NaOH.
For the given question sodium hydroxide solution dissociates to form positively charged sodium ions and negatively charged hydroxide ions.
 $ {\text{NaOH}} \to {\text{N}}{{\text{a}}^{\text{ + }}}{\text{ + O}}{{\text{H}}^{\text{ - }}} $
From the given information, the NaOH solution has a normality of $ 0.1 $ N which is equal to $ 0.1 $ M of NaOH, thus we can say that $ {\text{N}}{{\text{a}}^{\text{ + }}} $ and $ {\text{O}}{{\text{H}}^{\text{ - }}} $ also have a molarity of $ 0.1 $ M.
As we known that pOH (strength of base or OH) = -log ( $ {\text{O}}{{\text{H}}^{\text{ - }}} $ )
That is, $ pOH = - log(0.1){\text{ }} = 1 $
As we know $ pH + pOH = 14 $
 $ pH{\text{ }} = 14 - 1 $
pH = 13.
Therefore, we can say that the pH of a solution containing $ 0.1 $ N NaOH solution is 13.
Hence, the correct option will be option C – 13.

Note:
The scale of pH has a range of 14. If the value of pH for a solution is less than 7 then the solution is considered to be acidic. A solution with a pH value of 7 is neutral in nature while a solution having a pH of more than 7 is considered to be alkaline that is a basic solution. The pH of any solution can be measured using a pH meter. It is used for measuring the pH of drinking water, soils in agriculture, etc.