Question

What is the pH of a $1\text{ x 1}{{\text{0}}^{-4}}$ M HCl solution?

Answer 1

Hint: When the concentration of the solution is given then we can find the pH of the solution by using the relation as the pH of the solution is equal to the negative logarithm of the concentration of the hydrogen ions. This is written as:
$pH=-\log [{{H}^{+}}]$

Complete answer:
The given solution is oh hydrochloric acid (HCl) and we know that hydrochloric acid is a strong acid. As the strength of the acid increases its ionization also increases. So, when the Hydrochloric acid will be dissolved in water then it will dissociate into hydrogen ions and chloride ions. Since hydrochloric acid is a strong acid, it will dissociate fully into ions in the solution. Therefore, the concentration of the solution will be equal to the concentration of hydrogen ions in the solution.
So, the given concentration of the hydrochloric acid solution is $1\text{ x 1}{{\text{0}}^{-4}}$ M therefore, the concentration of hydrogen ions in the solution is $1\text{ x 1}{{\text{0}}^{-4}}$ M.
When the concentration of the solution is given then we can find the pH of the solution by using the relation as pH of the solution is equal to the negative logarithm of the concentration of the hydrogen ions. This is written as:
$pH=-\log [{{H}^{+}}]$
Now, putting the value in the formula, we get:
$pH=-\log [{{10}^{-4}}]$
$pH=-(-4)\log 10$
$pH=4\text{ x 1}$
Because log 10 is 1

The pH of the solution is 4. Since the pH of the solution is lesser than the 7, so the answer is correct.

Note:
If the concentration of the solution is equal to or less than ${{10}^{-8}}$ M of any acid, then we cannot easily calculate the pH of the solution by using this formula because the pH of an acidic solution cannot be greater than 7.