初中化学实验中有许多涉及实验操作的“先”与“后”的问题,这些问题,关系到化学实验的效果、实验的成败、实验操作的安全以及药品的有效使用等,同时也体现着对化学实验规则的了解、实验技能的掌握以及实验原理的理解和运用程度。因此,弄清这些问 There are many problems related to the “first” and “after” experiments in junior high school chemistry experiments. These problems are related to the effects of chemical experiments, the success or failure of experiments, the safety of experimental operations, and the effective use of medicines. It also embodies the understanding of chemical experiment rules, the mastery of experimental skills, and the degree of understanding and application of experimental principles. So, make sure of these questions