How can I write dissociation equations?
Well, you do it stoichiometrically.
Chemical reactions are characterized by two properties: (i) conservation of mass; and (ii) conservation of charge. If I start with 10 g of reactant (from all sources), AT MOST I can get 10 g of product. In fact, because of handling losses, I am not even going to get that. In addition, electrostatic charge is also conserved. Neutral reactants necessarily give neutral products. Cationic reactants give cationic products, etc.
So for dissociation of common salt in water:
Are mass and charged conserved in this reaction. What about the dissociation of magnesium nitrate?