Ammoniacal brine is a solution of ammonia (NH₃) in water (H₂O). It doesn't have a specific chemical formula, as the concentration of ammonia can vary greatly.

Here's how we can represent it:

* NH₃(aq): This is a general representation of ammonia dissolved in water. "aq" stands for aqueous, meaning it's in solution.

To be more specific, you'd need to know the molarity (moles of solute per liter of solution) or percentage by weight of ammonia in the solution. For example:

* 0.5 M NH₃(aq): This indicates a solution containing 0.5 moles of ammonia per liter of water.

* 10% NH₃(aq): This indicates a solution containing 10 grams of ammonia per 100 grams of solution.

Therefore, the chemical formula of ammoniacal brine is NH₃(aq), but the specific composition depends on the concentration of ammonia present.