How can we determine the Acidity or the base of a solution just from the information the molecular formula provides, like $\ce{KCl}$, $\ce{NH4Cl}$, $\ce{MgSO4}$, $\ce{NaCO3}$, like which ones have a pH of less or more than 7, if I was given the concentration , I would have used $-\log{\ce{[H3O+]}}$ formula, but without it, how can I determine the pH levels?


You cannot determine exact pH levels without knowing specific equilibrium constants (or equivalent values) and concentration of the substances.

Determining whether something is acidic is relatively straight forward. Inorganic compounds like the one you've presented can be broken down into cations and anions.

For the anions, you should consider:

  1. Is this anion acidic ($\ce{H2PO4-}$)
  2. Is this anion basic ($\ce{OH-}, \ce{HCO3-}$)

For the cations, you should consider:

  1. Is this cation the hydrogen ion ($\ce{H+}$)
  2. Is this cation a Brønsted-Lowry acid ($\ce{NH4+}$)
  3. Is this cation Lewis acidic ($\ce{Al^{3+}}$)

For compounds where ions are both acidic and basic, the exact balance matters. Then, you're crossing into the complicated regime where things are interesting.


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