How to determine if a given salt is of a weak acid or of a weak base ?

Salts of weak acids (e.g. sodium acetate) are composed from a negatively charged conjugate base (acetate) and a positively charged counter ion (sodium). A simple rule here is that if the counter ion is positively charged (e.g. sodium, potassium,  calcium, magnesium.... etc.) then the salt is for a weak acid. When salts of weak acids dissolve in water they completely ionize to produce the conjugate base (which acts as a base, and increases pH of solution) and the counter ion. examples on salts of weak acids include: potassium acetate, sodium sulfathiazole, and sodium barbiturate.

Salts of weak bases (e.g. ammonium chloride) are composed from a positively charged conjugate acid (ammonium) and a negatively charged counter ion (chloride). A simple rule here is that if the counter ion is negatively charged (e.g. chloride, bromide, sulphate...etc.) then the salt is for a weak base. When salts of weak bases dissolve in water they completely ionize to produce the conjugate acid (which acts as an acid, and reduces pH of solution) and the counter ion. Examples on salts of weak bases include: ammonium bromide, atropine sulphate, and ephedrine sulphate.

Some salts are composed from both a conjugate acid of a weak base and a conjugate base of a weak acid (e.g. ammonium acetate). These are considered salts of weak acids and weak bases.