Question

The $pH$ of ${10^{ - 4}}M{\text{ }}KOH$ solution will be:

Answer 1

Hint: $pH$ is a scale which is used to specify the acidity or basicity of a solution. Acidic solutions are measured to have lower $pH$ than basic solutions and it is measured in $moles{\text{ }}per{\text{ }}litre$.

Complete step by step answer:
$KOH$ is an inorganic compound which is commonly known as caustic potash and is a strong base. It appears to be colourless and has many industrial applications such as manufacturing of soaps, acting as an electrolyte in alkaline batteries etc.
We can determine the $pH$ of a solution using $pH$ to ${H^ + }$ formula:
$pH = - \log ([{H^ + }])$
Given, $[KOH] = [O{H^ - }] = {10^{ - 4}}M$
We know that,
$
  [{H^ + }][O{H^ - }] = 1 \times {10^{ - 14}} \\
  [{H^ + }] \times {10^{ - 4}} = 1 \times {10^{ - 14}} \\
  [{H^ + }] = \dfrac{{1 \times {{10}^{ - 14}}}}{{{{10}^{ - 4}}}} = 1 \times {10^{ - 4}}M \\
  \therefore pH = - \log [{H^ + }] = - \log (1 \times {10^{ - 10}}) = 10 \\
$

Therefore, the $pH$ of ${10^{ - 4}}M{\text{ }}KOH$ solution is option (D), $10$.

Note:
The $pH$ scale can expand in between $0{\text{ to }}1$ in a linear scale or compact scale into a large scale for comparison. The positive value of the $pH$ scale is because of the use of negative log$[{H^ + }]$. Although, we generally measure $pH$ in between $0{\text{ to }}14$, there is no upper limit or lower limit, since $pH$ is the concentration of ${H^ + }$.