[antonioo1995]

Hi everybody, I'm not American ( Australian, English etc   ) so sorry if something sounds strange

So guys I have this exercise :

Say, giving explanation , how the pH of an acidic aqueous solution varies for the addition of :
a) water ; b ) KCN ; c ) Sodium chloride ; d ) an aqueous solution of sodium sulfate .

I would like to understand, first of all, how to know if an acid or a base are strong or weak . Is there a more practical way to understand that, not memorizing all the different Ka of all compounds on earth ?  How can I know, for example, if a chemical element is the conjugate acid of a strong base if I don't know if the element itself is a strong or weak acid ?

And if you work out the exercise with all the steps I would be so thankful to you  ( please explain me also why water decreases or rises the concentration of H+ in solution) 

[Borek]

Learn the list of strong acids and bases (it is not that long). Everything else is weak.

You have to show your attempts at solving the question to receive help. This is a forum policy.

[antonioo1995]

I've studied that list and tried to do the exercise but I still don't manage to understand a few things, like for example why sodium solfate solo does not influence the pH while H2O does...please  I really need an explanation

[Arkcon]

OK, you still have some work to do organizing your question.  How concentrated of a solution of sodium sulfate?  How much of a pH difference between plain water and an aqueous solution?

[antonioo1995]

What do you mean? Do you need extra data? Unfortunately the exercise does not give other information  , but that should not be a problem cause it's just asking to make a prediction, not requiring the precise amount of pH formed 
But if you don't wanna work out the exercise not problem...just explain me what I've asked in the last reply please 

[Borek]

Why do you think addition of sodium sulfate doesn't change pH of the solution? First, it will dilute the solution just like pure water does, second, it will change ionic strength of the solution (no idea if you were already taught about the latter).

[antonioo1995]

   Cause the answer says: " Sodium sulfate has no effect , but by addition of the solution the concentration of H+ decreases "