Question

The pH of N/10 sodium hydroxide is--------.
(a) 12.0
(b) 2.0
(c) 1.0
(d) 13.0

Answer 1

Hint: We have been given the normality of NaOH solution, from this we will first the ${{\text{p}}_{OH}}$value of NaOH by the formula: ${{\text{p}}_{OH}}$= -log[OH] and after that by using this value we will find the pH of the NaOH solution by the formula : pH+${{\text{p}}_{OH}}$=14. Now solve it.

Complete step by step answer:
Before calculation of pH we should know what, it is: pH gives us the measure of acid/base strength of any solution. pH scale ranges from 0-14, 7 is neutral, below 7 it represents acidic and above 7 it represents basic.
Since, the solution is NaOH , which is basic in nature and thus it should have the value of pH more than 7 and it should be between 7 to 14.
Now, solving the numerical:
As we know that:
pH+${{\text{p}}_{OH}}$=14 ----(1)
sop first we have to find out the value of ${{\text{p}}_{OH}}$by using the formula as;
${{\text{p}}_{OH}}$= -log[OH] -------(2)
And the concentration of [OH]= $\dfrac{1}{10}$ N (given)
So, the value of concentration of [OH] in the equation (2), we get;
${{\text{p}}_{OH}}$= -log($\dfrac{1}{10}$)
= -log($1\times {{10}^{-1}}$)
= -(-log 10)
= log10
And as we know that from logarithm tables, log 10=1
Then,
${{\text{p}}_{OH}}$=1
Now, put this value in equation (1), we get:
pH+ 1=14
pH= 14 -1
=13
Hence, the pH of N/10 sodium hydroxide is 13.

Hence, option(d) is correct.

Note: You can’t directly find the concentration of the, ${{\text{p}}_{OH}}$ first you have to find the concentration of OH and then only you can find the value of ${{\text{p}}_{OH}}$ and then we can be able to find the pH value of NaOH ranging between 0-14.