Final answer:
Adding 1 M HCl dropwise allows for careful control over the reaction, safety, and attainment of specific ionic concentration needed for selective precipitation of certain compounds.
Step-by-step explanation:
It is important to add 1 M HCl dropwise to the crucible because this method of addition allows for controlled reactions, minimizing the risk of a too-rapid reaction that could result in an inaccurate determination of reaction completion, such as when a precipitate forms. This technique also aids in preventing safety hazards like splattering, which can occur due to the exothermic nature of acid-base reactions. Furthermore, gradual addition is essential when aiming for a specific concentration of ions in solution.