How can one calculate the pH of a solution?
I'm tring to write the methodology
If anything is wrong please point it out to me i'll be happy to correct!

To find $\small\ce{pH} $ of a solution you can:  


Find the conjugated base of your acid  (for example $\small\ce{HCOOH}$ becomes $\small\ce{HCOO-}$ (correct me if i'm wrong here)  
Write the equation of the solution
Now you want to prepare an aqueous solution. 
Find the concentration of $\small\ce{[CH_3COOH]}$ 
you use the formula to determine the concentration in solution of acid

$$
   \ce{[CH_3COOH]\ =\ C\ -\ [CH3COO- ]}
   $$

($\ce{C}$ is the concentration of brought acid in $\ce{mol/l}$)
Then you write that:  

$$\qquad\ce{[H+ ]\ =\ [CH3COO- ]}$$
as both dissociate from the same acid as 

$$\ce{CH3COOH\ -&gt;\ CH3COO- \ +\ H+}$$
the $\small\ce{pH}$ concentration is given by:
$$\ce{pH\ =\ -\log(\small[H_3O+ ])}$$ 


$pH$ here you are! (without any unit)