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有关化学反应方程式的计算,初中学生在掌握了计算的一般步骤之后,关键是遵循质量守恒定律确定“三量”,即确定隐藏在命题中反应物或生成物的已知量;确定过量问题中的不足量;确定不纯物质的纯量。下面谈谈我这方面教学的做法。一、直接运用质量守恒定律,确定隐藏在命题中的已知量。在综合性命题中,往往未明显地给出反应物或生成物的质量。解这类题,既要运用化学方程式计算的一般方法和步骤,又要熟悉、理解、应用有关的物质性质和有关概念,启发学生运用质量守恒定律,找出隐藏在题意中反应物或全成物的已知量。如:把干燥纯净的氯酸钾和二氧化锰的混和物15.6克装入大试管,给试管加热,制取氧气,反应后获得10.7克固体物质。问:制得的氧气多少克?原混和物中有多少克氯酸钾?10.7克团体物质中含有哪些物质?各多少克?此题没有明显地给出反应物或生成物的质量,而是将其隐藏在命题中,解题的关键是求出生成物氧气的质量,为此,应启发学生运用质量守恒定律,了解二氧化锰在此反应中的作用、催化剂的性质。使学生自己得出:反应前试管中混和物质量=反应后试管中混和物质量+生成的氧气质量即:
The calculation of the chemical reaction equation, junior high school students master the general steps in the calculation, the key is to follow the law of conservation of mass to determine the “three”, that is, to determine the known amount of reactants or products hidden in the proposition; Deficiencies; determine the purity of impure material. Here to talk about my teaching in this area. First, the direct use of the law of conservation of mass, to determine the hidden amount in the proposition. In comprehensive propositions, the quality of the reactants or products is often not clearly given. To solve such problems, we must not only use the general methods and steps of chemical equation calculation, but also be familiar with, understand and apply relevant physical properties and related concepts to inspire students to apply the law of conservation of mass to find out the hidden objects or complete Known amount of product. For example, 15.6 g of a dry, pure mixture of potassium chlorate and manganese dioxide was placed in a large test tube and the test tube was heated to make oxygen. After the reaction, 10.7 g of solid substance was obtained. Q: How many grams of oxygen is made? How many grams of potassium chlorate are in the original mixture? What is contained in 10.7 grams of the substance? What is the amount of grams? The question does not give a clear indication of the quality of the reactants or products. Instead, Hidden in the proposition, the key to solving the problem is to find the quality of the resultant oxygen. Therefore, students should be encouraged to use the law of conservation of mass to understand the role of manganese dioxide in this reaction and the nature of the catalyst. The students themselves: before the reaction in the test tube mixture mass = the amount of the mixture in the test tube after the reaction + the quality of oxygen generated by: