Calculate the concentration of H3O+ ions present in a solution of HCl that has a measured pH of 1.510 . M
HCl, the acid in Part 1, is a strong acid. The concentration of H3O+ ions in this solution is the same as the initial concentration of the acid.
A solution of the weak acid CH3COOH with the same initial concentration of acid will have a pH that is (Higer, lower, the same) the pH of the HCl solution.
Rank the following solutions in order of increasing acidity, placing the most acidic solution at the left. (CH3COOH is approximately 1.0% ionized at this concentration.)
pH= 0.00, pH= 7.45, [HCl]= .15M, [CH3COOH]= .15M
order of acidity
most acidic > least acidic

Solution :

The relationship between pH and  is pH =

The concentration of is given as

pH =

Therefore, the concentration of is

The relationship between pH and  is pH =

The concentration of is given as

pH =

    = 0.82

Therefore, the pH of the solution is 0.82

Now updating the ICE table for 0.15 M is as follows :

          0.15                                         0                      0

           -x                                           +x                    +x

         0.15 - x                                      x                      x

∴ Acidionization constant,

We can assume that :  (0.15 - x) M = 0.15 M

Therefore, from the equilibrium table,  

pH =

     = 2.77

Hence the pH of 0.15 M   is 2.77

Stronger acid always have a lower pH value.

The value of pH for the given solution are 0.0, 7.45, 0.82 and 2.77

So the increasing order of the acidity is :

pH = 0.0 > pH = 0.82 (0.15 M HCl) > pH = 2.77 (0.15 M ) > pH =7.45