How does an acid – base indicator such as methyl orange work in a system at equilibrium

How does an acid – base indicator such as methyl orange work in a system at equilibrium ? What is the dominant species of the indicator when the solution is acid or base? what will happened with the system at equilibrium when we add a acid solutions Like HCL or a base solution Like NaOH?NH4CL can dissolves. Can very soluble salts precipitate? Is he dissolution of NH4CL an endo or an exothermic process?Cobalt ions form the complex iOS Hexaaquacobalt (II) with water molecules.What is the dominant spices of cobalt at each step? Is the formation of the tetrachlorocobalt(II) complex an exothermic or an endothermic process?Are any other ways of shiffing this equilibrium?