Question

pH of ${10^{ - 6}}M$ HCl (aq) is
(A) just less than 6
(B) exactly equal to 6
(C) just greater than 6
(D) just less than 7

Answer 1

. In order to calculate the pH of hydrochloric acid, we must first have an idea about what a pH is. pH is a convenient way to measure the acidity and basicity of the solution. pH is a negative logarithm scale.

Complete step by step answer:
Let us first understand what pH is. 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 an acidic solution, pH is above 7 for basic solution and pH is equal to 7 for a neutral solution.
We can calculate the pH of hydrochloric acid by using the following formula:
$pH = - \log [{H^ + }]$
The $[{H^ + }]$ concentration of hydrochloric acid is given as ${10^{ - 6}}M$
Therefore,
$pH = - \log [{10^{ - 6}}]$
$pH = 6$
The pH of ${10^{ - 6}}M$ HCl (aq) is 6.
So, the correct answer is “Option B”.

Note: - We have to remember that pH and pOH are different from one another.
- The pH and pOH values are not the same for an acidic solution. When pH is below 7 for an acidic solution, then pOH will be below 7 for an acidic solution.
- The pH is above 7 for a basic solution while pOH is below 7 for a basic solution.