Distinction between Basic, Neutral, Acidic

[Rochelle Mosley 2D]

I am confused on the difference between these when not provided with the pH or Ka values. I did the practice test in the google drive for midterm 1, and it said that "given the two following salts, determine rather they are acidic, basic, or neutral?". For KF and RbNO3 and KF was basic and RbNO3 was neutral. And I am aware that one of the answers couldn't be acidic because the question states that they are salts. However, how would I distinguish between any compounds to classify if they are basic, neutral, or acidic without knowing their own pH or Ka values?

[Nicholas Flores 2F]

Hello!
To classify whether a salt will make a solution acidic, basic, or neutral you must remember the strong acids and bases. A salt that is made up of a strong acid and base will create a neutral solution due to the negligible effect it will have on the pH of the solution. This is because of the "seesaw" effect where a strong acid will have a weak conjugate base, and vice versa for strong bases. For example, RbNO3 is made up of the strong acid HNO3 and the strong acid RbOH or Rb2O. This means that NO3 is a weak conjugate base and Rb is a weak conjugate acid, therefore the solution will remain neutral when the salt RbNO3 is added. A salt made up of a strong base but a weak acid will make a solution acidic. For example, KF is made up of the strong base K2O or KOH (both strong bases) and the weak acid HF. Because the acid HF is weak, F will be a conjugate base that is not weak, meaning that KF will make the solution basic as F will form HF while K will disassociate to be K+ in the solution and have no effect on the acidity. A salt made up of a strong acid but a weak base will do the opposite, making a solution acidic due to the weak base having a strong conjugate acid. I hope this helps!