例题:如用第三周期的金属各1克跟足量的稀盐酸起反应,哪种金属置换出的氢气最多?哪种最少?通过计算说明。在教学中,指导学生运用列通式法来解此类题。找出其中规律,可以简化运算,提高效率,加深对知识的理解,也有利于提高学生分析问题、解决问题的能力。它所依据的原理是:虽然 Na、Mg、Al 化合价不同,但每摩尔金属所置换出的 H_2的质量或体积,都与它们的化合价成正比例关系,只要设金属元素为 R,原子量为 A,化合价为n,置换出的 H_2为 x 克,则任何金属与酸的置 Example: If 1 g of metal in the third cycle reacts with a sufficient amount of dilute hydrochloric acid, which metal will displace the most hydrogen? Which is the least? In the teaching, students are instructed to use the formula method to solve such problems. Finding out the rules can simplify the calculations, improve the efficiency, deepen the understanding of knowledge, and help students improve their ability to analyze problems and solve problems. It is based on the principle that although the valences of Na, Mg, and Al are different, the mass or volume of H2 displaced per mol of metal is directly proportional to their valence, provided that the metal element is R and the atomic weight is A, The valence is n, the displaced H 2 is x g, then any metal and acid