Question

$pH$ of $NaOH$ solution is $10$. What is the concentration of $NaOH$?

Answer 1

In order to obtain the concentration of NaOH, we can make use of the relationship between $pH$ and $pOH$, i.e.
$pH + pOH = 14$
By using the above equation, we can obtain$pOH$value, which will help us to find the concentration of NaOH easily.

Complete step by step solution:
In order to solve the above question, we must first convert the $pH$value into $pOH$. As it would be more convenient to obtain the concentration of NaOH. Because NaOH contains $O{H^ - }$ions. So, finding $pOH$ will make it easy to obtain the concentration.
Consider the equation,
$pH + pOH = 14$
We know that $pH$ of NaOH is given as 10, therefore equating in the above equation we get,
$10 + pOH = 14$
$pOH = 14 - 10 = 4$
$pOH = - \log [O{H^ - }]$
$4 = - \log [O{H^ - }]$
$- 4 = \log [O{H^ - }]$
Taking the antilog of the above equation will help us to get the concentration of NaOH.
${\rm{antilog[ - 4] = }}[O{H^ - }]$
$[O{H^ - }] = 0.0001M$

Therefore, the concentration of NaOH is 0.0001M.

Additional information:
- $pH$ is a convenient way to measure the acidity and basicity of the solution.
- $pH$ is a negative logarithm scale.
- Logarithm means for every one-unit change in the $pH$ scale, the concentration of
${H^ + }$ changes by 10 factors.
- For a temperature at $25^\circ C$, the $pH$ is below 7 for acidic solution, $pH$ is above 7 for basic solution and $pH$is equal to 7 for neutral solution.

Note: - The $pH$ and $pOH$ values are not the same for acidic solution. When $pH$ is below 7 for acidic solution, then $pOH$ will be below 7 for acidic solution.
- The $pH$ is above 7 for basic solution while $pOH$ is below 7 for basic solution.