pH calculation

[MichelleRamirez_2F]

When we are loking for pH why is pH= log10[H30]? How do we know what the value of [H3O] is?

[Tiffany_Cacy_3D]

Usually this value is given to you as the molarity of the solution or you are given moles and volume of a certain solution and you have to find the molarity by dividing moles of solute by liters of solution to find the molarity to in turn plug into the pH equation.

[Tony Chung 2I]

This is normally given to you in the problem as a molarity

[Lydia Luong 4L]

The molarity is usually given to you!

[Michael_Navarro_1H]

To clarify, if you are dealing with a strong acid, the molarity of the acid will equal the molarity of the H3O+ in solution. So for example, if you were given a solution of HCl with molarity 0.20 M and were asked to calculate the pH of the solution, the molarity of the H3O+ ions in solution would also be 0.20 M and the pH would be determined using -log[0.20].