Question

What is the pH of 1M HCl?
(A) 0
(B) 1
(C) 2
(D) 3

Answer 1

The formula to find the pH of the solution is as below.
$pH=-\log [{{H}^{+}}]$
Hydrochloric acid is a monoprotic acid, so it will give one proton upon dissociation in water.

Complete step by step solution:
We will first see how HCl dissociates in order to find how many protons it can give. Then, we will use the formula of pH in this solution.
-HCl will dissolve into proton and chloride ions upon dissociation in aqueous media. The reaction can be given as:
$HC{{l}_{(aq)}}\to {{H}^{+}}_{(aq)}+C{{l}^{-}}_{(aq)}$
-We can see that one mole of HCl gives one mole of ${{H}^{+}}$ ions. So, here we are given that the concentration of HCl in the solution is 1M. So, upon its dissociation, it will give 1M ${{H}^{+}}$ ions. Now, this concentration of ${{H}^{+}}$ ions will be useful in determining the pH of the solution.
The formula to find the pH of the solution is as below.
$pH=-{{\log }_{10}}[{{H}^{+}}]$
We have already obtained that the concentration of ${{H}^{+}}$ ions in the solution will be equal to 1M. So, we will put that value in the formula of pH. So, we get
$pH=-{{\log }_{10}}[1]$
Now, we can write 1 as ${{10}^{0}}$ because $1={{10}^{0}}$. So,
$pH=-\log [{{10}^{0}}]$
Now, we know that $\log [{{10}^{x}}]=x$. So,
$pH=0$
Thus, we obtained that pH of the 1M solution of HCl is 0.

So, the correct answer is (A).

Note: Do not get confused as the answer is zero because Sorenson proposed a pH scale of 1 to 14. It is possible for a 1M solution of HCl that the pH is zero. Actually if the concentration increases than 1M for HCl solution, then pH we obtain is in a negative value.